Optical device, laser beam source, laser apparatus and method of producing optical device

ABSTRACT

After forming domain inverted layers  3  in an LiTaO 3  substrate  1,  an optical waveguide is formed. By performing low-temperature annealing for the optical wavelength conversion element thus formed, a stable proton exchange layer  8  is formed, where an increase in refractive index generated during high-temperature annealing is lowered, thereby providing a stable optical wavelength conversion element. Thus, the phase-matched wavelength becomes constant, and variation in harmonic wave output is eliminated. Consequently, with respect to an optical wavelength conversion element utilizing a non-linear optical effect, a highly reliable element is provided.

TECHNICAL FIELD

[0001] The present invention relates to an optical element such as anoptical wavelength conversion element, a laser light source and a laserdevice suitable for use in the field of optical information processingor optical measuring control where coherent light is used, and alsorelates to a method for producing an optical element.

BACKGROUND ART

[0002] Referring to FIG. 1, a conventional laser light source using anoptical wavelength conversion element will be described. The laser lightsource is basically composed of a semiconductor laser 20, a solid statelaser crystal 21 and an optical wavelength conversion element 25 made ofKNbO₃, which is a non-linear optical crystal.

[0003] As shown in FIG. 1, pumped light P1 a emitted from thesemiconductor laser 20, which oscillates at 807 nm, is collected by alens 30 so as to excite YAG as a solid state laser crystal 21. A totalreflection mirror 22 is formed on an incident surface of the solid statelaser crystal 21. The total reflection mirror reflects 99% of lighthaving a wavelength of 947 nm but transmits light in the 800 nmwavelength band. Although the pumped light P1 a is thus efficientlyintroduced into the solid state laser crystal 21, the light with awavelength of 947 nm, which is generated by the solid state lasercrystal 21, is reflected to the optical wavelength conversion element 25side without being emitted to the semiconductor laser 20 side. Moreover,a mirror 23, which reflects 99% of light having a wavelength of 947 nmbut transmits light in the 400 nm wavelength band, is provided on theoutput side of the optical wavelength conversion element 25. Thesemirrors 22 and 23 form a resonator (cavity) for light having awavelength of 947 nm, capable of generating oscillation at 947 nm as afundamental wave P1.

[0004] The optical wavelength conversion element 25 is inserted in thecavity defined by the mirrors 22 and 23, whereby a harmonic wave P2 isgenerated. The power of the fundamental wave P1 within the cavityreaches to 1 W or higher. Therefore, the conversion from the fundamentalwave P1 to the harmonic wave P2 is increased, whereby a harmonic wavehaving a high power can be obtained. A harmonic wave of 1 mW can beobtained by using a semiconductor laser having an output of 500 mW.

[0005] Next, referring to FIG. 2, a conventional optical wavelengthconversion element having an optical waveguide will be described. Theillustrated optical wavelength conversion element, when a fundamentalwave having a wavelength of 840 nm is incident thereupon, generates asecondary harmonic wave (wavelength: 420 nm) corresponding to thefundamental wave. Such an optical wavelength conversion element isdisclosed in K. Mizuuchi, K. Yamamoto and T. Taniuchi, Applied PhysicsLetters, Vol 58, p. 2732, June 1991.

[0006] As shown in FIG. 2, in this optical wavelength conversionelement, an optical waveguide 2 is formed in an LiTaO₃ substrate 1, withlayers whose polarization is inverted (domain inverted layers) 3 beingperiodically arranged along the optical waveguide 2. Portions of theLiTaO₃ substrate 1 where the domain inverted layer 3 is not formed willserve as a domain non-inverted layer 4.

[0007] When the fundamental wave P1 is incident upon one end (anincident surface 10) of the optical waveguide 2, the harmonic wave P2 iscreated in the optical wavelength conversion element and is output fromthe other end of the optical waveguide 2. At this point, lightpropagating through the optical waveguide 2 is influenced by a periodicstructure formed by the domain inverted layers 3 and the domainnon-inverted layer 4, whereby propagation constant mismatching betweenthe generated harmonic wave P2 and the fundamental wave P1 iscompensated by the periodic structure of the domain inverted layers 3and the domain non-inverted layer 4. As a result, the optical wavelengthconversion element is able to output the harmonic wave P2 with a highefficiency.

[0008] Such an optical wavelength conversion element includes, as abasic component, the optical waveguide 2 produced by a proton exchangemethod.

[0009] Hereinafter, referring to FIG. 3, a method for producing such anoptical wavelength conversion element will be described.

[0010] First, at step S10 in FIG. 3, a domain inverted layer formationstep is performed.

[0011] More particularly, a Ta film is first deposited so as to coverthe principal surface of the LiTaO₃ substrate 1, after which ordinaryphotolithography and dry etching techniques are used to pattern the Tafilm into a striped pattern, thereby forming the Ta mask.

[0012] Next, a proton exchange process is performed at 260° C. for 20minutes for the LiTaO₃ substrate 1 whose principal surface is covered bythe Ta mask. Thus, 0.5 μm thick proton exchange layers are formed inportions of the LiTaO₃ substrate 1 which are not covered by the Ta mask.Then, the Ta mask is removed by etching for 2 minutes using a mixturecontaining HF:HNF₃ at 1:1.

[0013] Next, a domain inverted layer is formed within each of the protonexchange layers by performing a heat treatment at 550° C. for 1 minute.In the heat treatment, the temperature rise rate is 50° C./sec and thecooling rate is 10° C./sec. In portions of the LiTaO₃ substrate 1 wherethe proton exchange has been performed, the amount of Li is reduced ascompared to that in other portions thereof where the proton exchange hasnot been performed. Therefore, the Curie temperature of the protonexchange layer decreases, whereby the domain inverted layer can beformed partially in the proton exchange layer at a temperature of 550°C. This heat treatment allows for formation of the proton exchange layerhaving a pattern upon which the pattern of the Ta mask is reflected.

[0014] Next, at step 2 in FIG. 3, an optical waveguide formation step isperformed.

[0015] More particularly, step 2 is generally divided into step S21,step S22 and step S23. The mask pattern is formed at step S21; theproton exchange process is performed at step S22; and high-temperatureannealing is performed at step S23.

[0016] These steps will be described below.

[0017] At step S21, the Ta mask used for forming the optical waveguideis formed. The Ta mask is obtained by forming slit-shaped openings(width: 4 μm, length: 12 mm) in a Ta film. At step S22, a highrefractive index layer (thickness: 0.5 μm) linearly extending in onedirection is formed in the LiTaO₃ substrate 1 by performing a protonexchange process at 260° C. for 16 minutes for the LiTaO₃ substrate 1which is covered by the Ta mask. The high refractive index layer willeventually function as an optical waveguide. However, the non-linearityof the portions where the proton exchange has been performed (the highrefractive index layers), as thus formed, is deteriorated. In order torestore the non-linearity, annealing is performed at 420° C. for 1minute at step S22 after removing the Ta mask. This annealing expandsthe high refractive index layer in the vertical direction and in thelateral direction, thereby diffusing Li into the high refractive indexlayers. By reducing the proton exchange concentration in the highrefractive index layers in this way, it is possible to restore thenon-linearity. As a result, the refractive index of the regions locateddirectly under the slits of the Ta mask (the high refractive indexlayers) is increased by about 0.03 from the refractive index in otherregions, whereby the high refractive index layers function as an opticalwaveguide.

[0018] Next, a protective film formation step (step S30), an end facepolishing step (step S40), and an AR coating step (step S50) areperformed, thereby completing an optical wavelength conversion element.

[0019] By setting the arrangement pitch of the domain inverted layersperiodically arranged along the waveguide to 10.8 μm, it is possible toform a third-order pseudo phase-matched structure.

[0020] With the above-described optical wavelength conversion element,when the length of the optical waveguide 2 is set to 9 mm, the harmonicwave P2 having a power of 0.13 mW can be obtained for the fundamentalwave P1 (power: 27 mW) having a wavelength of 840 nm (conversionefficiency: 0.5%).

[0021] For forming a first-order pseudo phase-matched structure, thearrangement pitch of the domain inverted layers can be set to 3.6 μm. Inthis case, the harmonic wave P2 of 0.3 mW can be obtained for thefundamental wave P1 of 27 mW (conversion efficiency: 1%). The inventorsof the present invention have experimentally produced a laser lightsource which outputs blue laser light by combining such an opticalwavelength conversion element with a semiconductor laser.

[0022] Such an optical wavelength conversion element has a problem thatthe phase-matched wavelength thereof varies with the passage of time,whereby a harmonic wave cannot be obtained. When the wavelength of thefundamental wave emitted from a semiconductor laser is kept constant,but the phase-matched wavelength of the optical wavelength conversionelement is shifted, the harmonic wave output will gradually decrease,and it will eventually becomes zero.

[0023] The object of the present invention is to stabilize a laser lightsource, to increase the output thereof, and to reduce the size andweight of a laser device or an optical disk apparatus by incorporating ahigh output laser light source into these devices/apparatuses.

DISCLOSURE OF THE INVENTION

[0024] A method for producing an optical element of the presentinvention includes: a step of forming a proton exchange layer in anLiNb_(X)Ta_(1−X)O₃ (0≦X≦1) substrate; and an annealing step ofperforming a heat treatment for the substrate at a temperature of 120°C. or lower for 1 hour or more.

[0025] Preferably, the annealing step is performed at a temperatureequal to or higher than 50° C. but lower than or equal to 90° C.

[0026] The annealing step may include a step of gradually lowering thetemperature.

[0027] In one embodiment, the step of forming the proton exchange layerincludes: a step of performing a proton exchange process for thesubstrate; and a step of performing a heat treatment for the substrateat a temperature of 150° C. or higher.

[0028] In one embodiment, the step of forming the proton exchange layerincludes: a step of forming a plurality of periodically-arranged domaininverted layers in the substrate; and a step of forming an opticalwaveguide on a surface of the substrate.

[0029] Another method for producing an optical element of the presentinvention includes: a step of performing a proton exchange process foran LiNb_(X)Ta_(1−X)O₃ (0≦X≦1) substrate; and an annealing step ofperforming a plurality of heat treatments including at least first andsecond heat treatments for the substrate. The temperature of the secondannealing is lower than the temperature of the first annealing by 200°C. or more.

[0030] Preferably, the second annealing is performed at a temperatureequal to or higher than 50° C. but lower than or equal to 90° C.

[0031] An optical element of the present invention includes anLiNb_(X)Ta_(1−X)O₃ (0≦X≦1) substrate and a proton exchange layer formedin the substrate. The optical element is formed of a stable protonexchange layer such that a refractive index of the proton exchange layerdoes not vary with time during operation.

[0032] In one embodiment, at least a portion of the proton exchangelayer forms an optical waveguide.

[0033] A light source of the present invention includes: a semiconductorlaser; and an optical wavelength conversion element for receiving laserlight emitted from the semiconductor laser so as to convert the laserlight to a harmonic wave. The optical wavelength conversion elementincludes: an optical waveguide for guiding the laser light; and domaininverted structures periodically arranged along the optical waveguide,the optical waveguide and the domain inverted structures being formed ofa stable proton exchange layer whose refractive index does not vary withtime during operation.

[0034] Another laser light source of the present invention includes: asemiconductor laser for emitting a fundamental wave; a single mode fiberfor conveying the fundamental wave; and an optical wavelength conversionelement for receiving the fundamental wave emitted from the fiber so asto generate a harmonic wave, the optical wavelength conversion elementhaving periodic domain inverted structures.

[0035] In one embodiment, the optical wavelength conversion element hasa modulation function.

[0036] Preferably, the optical wavelength conversion element is formedin an LiNb_(X)Ta_(1−X)O₃ (0≦X≦1) substrate.

[0037] Still another laser light source of the present inventionincludes: a semiconductor laser for emitting a pumped light; a fiber forconveying the pumped light; a solid state laser crystal for receivingthe pumped light emitted from the fiber so as to generate a fundamentalwave; and an optical wavelength conversion element for receiving thefundamental wave so as to generate a harmonic wave, the opticalwavelength conversion element having periodic domain invertedstructures.

[0038] Preferably, the optical wavelength conversion element has amodulation function.

[0039] Preferably, the optical wavelength conversion element is formedin an LiNb_(X)Ta_(1−X)O₃ (0≦X≦1) substrate.

[0040] In one embodiment, the solid state laser crystal and the opticalwavelength conversion element are integrated together.

[0041] Still another laser light source of the present inventionincludes: a semiconductor laser for emitting a pumped light; a solidstate laser crystal for receiving the pumped light so as to generate afundamental wave; a single mode fiber for conveying the fundamentalwave; and an optical wavelength conversion element for receiving thefundamental wave from the fiber so as to generate a harmonic wave, theoptical wavelength conversion element having periodic domain invertedstructures.

[0042] Preferably, the optical wavelength conversion element has amodulation function.

[0043] Still another laser light source of the present inventionincludes: a distributed feedback type semiconductor laser for emittinglaser light; a semiconductor laser amplifier for amplifying the laserlight; and an optical wavelength conversion element for receiving theamplified laser light so as to generate a harmonic wave, the opticalwavelength conversion element having periodic domain invertedstructures.

[0044] Preferably, the optical wavelength conversion element has amodulation function.

[0045] Preferably, the optical wavelength conversion element is formedin an LiNb_(X)Ta_(1−X)O₃ (0≦X≦1) substrate.

[0046] In one embodiment, the semiconductor laser is wavelength-locked.

[0047] Still another laser light source of the present inventionincludes: a semiconductor laser for emitting laser light; and an opticalwavelength conversion element in which periodic domain invertedstructures and an optical waveguide are formed. The width and thethickness of the optical waveguide are each 40 μm or greater.

[0048] A laser light source according to claim 26, wherein the opticalwavelength conversion element has a modulation function.

[0049] The optical wavelength conversion element is formed in anLiNb_(X)Ta_(1−X)O₃ (0≦X≦1) substrate.

[0050] In one embodiment, the optical waveguide is of a graded type.

[0051] A laser device of the present invention includes: a laser lightsource having a semiconductor laser for radiating laser light and anoptical wavelength conversion element for generating a harmonic wavebased on the laser light; a modulator for modulating an output intensityof the harmonic wave; and a deflector for changing a direction of theharmonic wave emitted from the laser light source. Periodic domaininverted structures are formed in the optical wavelength conversionelement.

[0052] In one embodiment, a harmonic wave is superimposed over thesemiconductor laser during operation.

[0053] In one embodiment, the laser light source includes a single modefiber for conveying laser light from the semiconductor laser to theoptical wavelength conversion element.

[0054] In one embodiment, the laser light source includes: a fiber forconveying laser light from the semiconductor laser; and a solid statelaser crystal for receiving laser light emitted from the fiber so as togenerate a fundamental wave.

[0055] In one embodiment, the semiconductor laser device is adistributed feedback type semiconductor laser; and the laser lightsource further comprises a semiconductor laser amplifier for amplifyingthe laser light from the distributed feedback type semiconductor laser.

[0056] In one embodiment, an optical waveguide is formed in the opticalwavelength conversion element; and the width and the thickness of theoptical waveguide are each 40 μm or greater.

[0057] Another laser device of the present invention includes: a laserlight source for radiating modulated ultraviolet laser light; and adeflector for changing a direction of the ultraviolet laser light. Thedeflector irradiates a screen with the ultraviolet laser light so as togenerate red, green or blue light from a fluorescent substance beingapplied on the screen.

[0058] In one embodiment, the laser light source includes: asemiconductor laser; an optical wavelength conversion element forgenerating a harmonic wave; and a single mode fiber for conveying laserlight from the semiconductor laser to the optical wavelength conversionelement.

[0059] In one embodiment, the laser light source includes: asemiconductor laser; a fiber for conveying laser light from thesemiconductor laser; a solid state laser crystal for receiving laserlight emitted from the fiber so as to generate a fundamental wave; andan optical wavelength conversion element for generating a harmonic wavefrom the fundamental wave.

[0060] In one embodiment, the laser light source further includes: asemiconductor laser; and a semiconductor laser amplifier for amplifyinglaser light from a distributed feedback type semiconductor laser.

[0061] In one embodiment, the laser light source includes: asemiconductor laser for emitting laser light; and an optical wavelengthconversion element in which an optical waveguide for guiding the laserlight and periodic domain inverted structures are formed. The width andthe thickness of the optical waveguide are each 40 μm or greater.

[0062] Still another laser device of the present invention includes:three laser light sources for generating red, green and blue laser lightbeams; a modulator for changing an intensity of each of the laser lightbeams; and a deflector for changing a direction of each of the laserlight beams. The laser light source is formed of a semiconductor laser.

[0063] In one embodiment, a harmonic wave is superimposed over thesemiconductor laser during operation.

[0064] In one embodiment, the laser light source includes: asemiconductor laser; an optical wavelength conversion element forgenerating a harmonic wave; and a single mode fiber for conveying laserlight from the semiconductor laser to the optical wavelength conversionelement.

[0065] In one embodiment, the laser light source includes: asemiconductor laser; a fiber for conveying laser light from thesemiconductor laser; a solid state laser crystal for receiving laserlight emitted from the fiber so as to generate a fundamental wave; andan optical wavelength conversion element for generating a harmonic wavefrom the fundamental wave.

[0066] In one embodiment, the laser light source further includes: asemiconductor laser; and a semiconductor laser amplifier for amplifyinglaser light from a distributed feedback type semiconductor laser.

[0067] In one embodiment, the laser light source includes: asemiconductor laser for emitting laser light; and an optical wavelengthconversion element in which an optical waveguide for guiding the laserlight and periodic domain inverted structures are formed. The width andthe thickness of the optical waveguide are each 40 μm or greater.

[0068] Still another laser device of the present invention includes: atleast one laser light source including a semiconductor laser; asub-semiconductor laser; a modulator for changing an intensity of lightfrom the laser light source; a screen; and a deflector for changing adirection of light from the laser light source so as to scan the screenwith the light. Light emitted from the sub-semiconductor laser scans aperipheral portion of the screen; and radiation of laser light from thelaser light source is terminated when an optical path of the lightemitted from the sub-semiconductor laser is blocked.

[0069] In one embodiment, the laser light source includes: an opticalwavelength conversion element for generating a harmonic wave; and asingle mode fiber for conveying laser light from the semiconductor laserto the optical wavelength conversion element.

[0070] In one embodiment, the laser light source includes: thesemiconductor laser; a fiber for conveying laser light from thesemiconductor laser; a solid state laser crystal for receiving laserlight emitted from the fiber so as to generate a fundamental wave; andan optical wavelength conversion element for generating a harmonic wavefrom the fundamental wave.

[0071] In one embodiment, the semiconductor laser is a distributedfeedback type semiconductor laser; and the laser light source furtherincludes a semiconductor laser amplifier for amplifying laser light fromthe distributed feedback type semiconductor laser.

[0072] In one embodiment, the laser light source includes an opticalwavelength conversion element in which an optical waveguide for guidinglaser light from the semiconductor laser and periodic domain invertedstructures are formed. The width and the thickness of the opticalwaveguide are each 40 μm or greater.

[0073] A laser device of the present invention includes: at least onelaser light source including a semiconductor laser; a deflector forchanging a direction of laser light radiated from the laser light sourceso as to scan the screen with the laser light. The device furthercomprises two or more detectors for generating a signal when receiving aportion of the laser; and generation of laser light from the laser lightsource is terminated when the detector does not generate a signal for acertain period of time while the deflector scans the screen with thelaser light.

[0074] In one embodiment, the laser light source includes: an opticalwavelength conversion element for generating a harmonic wave; and asingle mode fiber for conveying laser light from the semiconductor laserto the optical wavelength conversion element.

[0075] In one embodiment, the laser light source includes: thesemiconductor laser; a fiber for conveying laser light from thesemiconductor laser; a solid state laser crystal for receiving laserlight emitted from the fiber so as to generate a fundamental wave; andan optical wavelength conversion element for generating a harmonic wavefrom the fundamental wave.

[0076] In one embodiment, the semiconductor laser is a distributedfeedback type semiconductor laser; and the laser light source furtherincludes a semiconductor laser amplifier for amplifying laser light fromthe distributed feedback type semiconductor laser.

[0077] In one embodiment, the laser light source includes an opticalwavelength conversion element in which an optical waveguide for guidinglaser light from the semiconductor laser and periodic domain invertedstructures are formed. The width and the thickness of the opticalwaveguide are each 40 μm or greater.

[0078] Still another laser device of the present invention includes: atleast one laser light source including a semiconductor laser; amodulator for changing an intensity of each laser light; and a deflectorfor changing a direction of each laser light. Laser light emitted fromthe laser light source is split into two or more optical paths so as toirradiate a screen from two directions.

[0079] In one embodiment, the laser light source includes: an opticalwavelength conversion element for generating a harmonic wave; and asingle mode fiber for conveying laser light from the semiconductor laserto the optical wavelength conversion element.

[0080] In one embodiment, the laser light source includes: thesemiconductor laser; a fiber for conveying laser light from thesemiconductor laser; a solid state laser crystal for receiving laserlight emitted from the fiber so as to generate a fundamental wave; andan optical wavelength conversion element for generating a harmonic wavefrom the fundamental wave.

[0081] In one embodiment, the semiconductor laser is a distributedfeedback type semiconductor laser; and the laser light source furtherincludes a semiconductor laser amplifier for amplifying laser light fromthe distributed feedback type semiconductor laser.

[0082] In one embodiment, the laser light source includes an opticalwavelength conversion element in which an optical waveguide for guidinglaser light from the semiconductor laser and periodic domain invertedstructures are formed. The width and the thickness of the opticalwaveguide are each 40 μm or greater.

[0083] In one embodiment, two optical paths are formed by two laserlight sources; and the laser light sources respectively experiencedifferent modulations.

[0084] In one embodiment, the two optical paths are switched with eachother based on time.

[0085] Still another laser device of the present invention includes atleast one laser light source including a semiconductor laser; a firstoptical system for setting laser light emitted from the laser lightsource into a parallel beam; a liquid crystal cell for spatiallymodulating the parallel beam; and a second optical system forirradiating a screen with light emitted from the liquid crystal cell.

[0086] In one embodiment, the laser light source includes: an opticalwavelength conversion element for generating a harmonic wave; and asingle mode fiber for conveying laser light from the semiconductor laserto the optical wavelength conversion element.

[0087] In one embodiment, the laser light source includes: thesemiconductor laser; a fiber for conveying laser light from thesemiconductor laser; a solid state laser crystal for receiving laserlight emitted from the fiber so as to generate a fundamental wave; andan optical wavelength conversion element for generating a harmonic wavefrom the fundamental wave.

[0088] In one embodiment, the semiconductor laser is a distributedfeedback type semiconductor laser; and the laser light source furtherincludes a semiconductor laser amplifier for amplifying laser light fromthe distributed feedback type semiconductor laser.

[0089] In one embodiment, the laser light source includes an opticalwavelength conversion element in which an optical waveguide for guidinglaser light from the semiconductor laser and periodic domain invertedstructures are formed. The width and the thickness of the opticalwaveguide are each 40 μm or greater.

[0090] In one embodiment, the sub-semiconductor laser is an infraredlaser.

[0091] In one embodiment, laser light radiation is terminated byshifting a phase-matched wavelength of the optical wavelength conversionelement.

[0092] An optical disk apparatus of the present invention includes: alaser light source for generating laser light; an optical wavelengthconversion element for converting a fundamental wave to a harmonic wave;an optical pickup incorporating therein the optical wavelengthconversion element; and an actuator for moving the optical pickup. Thelaser light radiated from the laser light source is incident upon theoptical pickup via an optical fiber.

[0093] In one embodiment, the laser light source includes asemiconductor laser disposed outside the optical pickup.

[0094] In one embodiment, the laser light source further includes asolid state laser crystal for generating a fundamental wave using laserlight emitted from the semiconductor laser as pumped light.

[0095] In one embodiment, the solid state laser crystal is disposedoutside the optical pickup; and the fundamental wave generated by thesolid state laser medium is incident upon the optical wavelengthconversion element via the optical fiber.

[0096] In one embodiment, the solid state laser crystal is disposedinside the optical pickup; and the laser light emitted from thesemiconductor laser is incident upon the solid state laser via theoptical fiber.

BRIEF DESCRIPTION OF THE DRAWINGS

[0097]FIG. 1 is a diagram illustrating a conventional short wavelengthlight source.

[0098]FIG. 2 is a diagram illustrating a structure of a conventionaloptical wavelength conversion element.

[0099]FIG. 3 is a flow chart illustrating steps of a method forproducing an optical wavelength conversion element according to aconventional method.

[0100]FIG. 4 is a graph illustrating temporal variation of a harmonicwave output of the conventional optical wavelength conversion element.

[0101]FIG. 5 is a graph illustrating temporal variation of aphase-matched wavelength of the conventional optical wavelengthconversion element.

[0102]FIG. 6 is a graph illustrating temporal variation of a refractiveindex of a conventional optical element.

[0103]FIG. 7 is a diagram illustrating a structure of an opticalwavelength conversion element according to Example 1 of the presentinvention.

[0104]FIGS. 8A, 8B, 8C, 8D and 8E are diagrams illustrating respectivesteps of a method for producing the optical wavelength conversionelement according to Example 1 of the present invention.

[0105]FIG. 9 is a flow chart illustrating steps of a method forproducing the optical wavelength conversion element according to Example1 of the present invention.

[0106]FIG. 10 is a characteristic diagram illustrating phase-matchedwavelength variation with respect to the annealing time, with theannealing time being a parameter.

[0107]FIG. 11 is a characteristic diagram illustrating the relationshipbetween the annealing temperature and the amount of phase-matchedwavelength variation.

[0108]FIG. 12 is a graph illustrating the output-time characteristic ofthe optical wavelength conversion element according to Example 1 of thepresent invention.

[0109]FIG. 13 is a graph illustrating temporal characteristics of thephase-matched wavelength and the effective refractive index of theoptical wavelength conversion element according to Example 1 of thepresent invention.

[0110]FIG. 14 is a flow chart illustrating steps of a method forproducing an optical wavelength conversion element according to Example2 of the present invention.

[0111]FIGS. 15A, 15B and 15C are diagrams illustrating respective stepsof a method for producing an optical element according to Example 4 ofthe present invention.

[0112]FIG. 16 is a flow chart illustrating steps of a method forproducing an optical element according to Example 5 of the presentinvention.

[0113]FIG. 17 is a diagram illustrating a configuration of an example ofa laser light source according to the present invention.

[0114]FIGS. 18A, 18B, 18C and 18D are diagrams illustrating respectiveproduction steps of the optical wavelength conversion element in thelaser light source of the present invention.

[0115]FIG. 19 is a graph illustrating the relationship between theoptical waveguide thickness and the endurance property against opticaldamage of the optical wavelength conversion element used in the laserlight source of the present invention.

[0116]FIG. 20 is a diagram illustrating a configuration of a laserdevice according to an example of the present invention.

[0117]FIG. 21 is a diagram illustrating a configuration of a laser lightsource according to an example of the present invention.

[0118]FIG. 22 is a diagram illustrating a configuration of asemiconductor laser used for a laser light source according to anexample of the present invention.

[0119]FIG. 23 is a diagram illustrating a configuration of a laser lightsource according to an example of the present invention.

[0120]FIG. 24 is a diagram illustrating a configuration of a laser lightsource according to an example of the present invention.

[0121]FIG. 25 is a diagram illustrating a configuration of a laser lightsource of a separate type according to an example of the presentinvention.

[0122]FIG. 26 is a diagram illustrating a configuration of a laser lightsource according to an example of the present invention.

[0123]FIG. 27 is a diagram illustrating a configuration of a laserdevice according to an example of the present invention.

[0124]FIG. 28 is a diagram illustrating a configuration of an automaticshutdown device for a laser device according to an example of thepresent invention.

[0125]FIG. 29 is a diagram illustrating a control system for theautomatic shutdown device for a laser device according to an example ofthe present invention.

[0126]FIG. 30 is a diagram illustrating a configuration of a laserdevice according to an example of the present invention.

[0127]FIG. 31 is a diagram illustrating a configuration of a laserdevice according to an example of the present invention.

[0128]FIG. 32 is a diagram illustrating a configuration of a laserdevice according to an example of the present invention.

[0129]FIG. 33 is a diagram illustrating a configuration of an opticaldisk apparatus according to an example of the present invention.

BEST MODE FOR CARRYING OUT THE INVENTION

[0130] The inventors of the present invention studied, with respect tothe above-described optical wavelength conversion element having anoptical waveguide, the cause of why the phase-matched wavelength thereofbecomes shorter with the passage of time, whereby a harmonic wave cannotbe generated.

[0131]FIG. 4 illustrates the relationship in the conventional opticalwavelength conversion element between the elapsed time immediately afterthe production of the element and the harmonic wave output thereof. Itcan be seen that the harmonic wave output rapidly decreases with thepassage of time.

[0132]FIG. 5 illustrates the relationship between the elapsed time andthe phase-matched wavelength. The harmonic wave output decreases to halfafter 3 days from immediately after the production of the element. Itcan be seen that, at this point of time, the phase-matched wavelengthhas shifted toward the short wavelength side. The phase-matchedwavelength λ is defined by a domain inversion pitch Λ and effectiverefractive indices n_(2W) and n_(W) respectively for a harmonic wave anda fundamental wave. More particularly, λ=2(n_(2W)−n_(W))·ΛA.

[0133] Since the pitch Λ of domain inverted layers does not vary withtime but is kept constant, the decrease in the phase-matched wavelengthλ is considered to result from variation in the effective refractiveindices n_(2W) and n_(W).

[0134]FIG. 6 illustrates the relationship between the effectiverefractive index n_(2W) and the elapsed time. It can be seen from FIG. 6that the effective refractive index n₂W decreases as more days elapsefrom the day when the element was produced.

[0135] The inventors of the present invention consider the causetherefor to be as follows.

[0136] The high temperature treatment at about 400° C. which isperformed when forming an optical waveguide introduces some strain, orthe like, into a proton exchange layer, whereby a layer with anincreased refractive index (the altered layer) is formed in the protonexchange layer. The strain is released gradually with the passage oftime, so that the refractive index of the altered layer becomes closerto the original refractive index thereof.

[0137] Although the altered layer with an increased refractive index isformed due to the strain, or the like, which is generated during thehigh temperature annealing, the refractive index of the altered layerreturns to the original magnitude thereof and, eventually, the alteredlayer becomes a stable proton exchange layer. However, it takes yearsfor the altered layer to become such a stable proton exchange layer. Inthe specification of the present application, a proton exchange layerwhose effective refractive index does not decrease with time, when usedat an ordinary temperature (about 0° C. to about 50° C.), is referred toas a “stable proton exchange layer”.

[0138] The above is the mechanism for the temporal variation suggestedby the inventors of the present invention. In order to confirm this, asample whose refractive index has lowered due to the temporal variationwas annealed at 300° C. for 1 minute. Such annealing temperature andannealing time will scarcely cause diffusion of proton, etc., and thewaveguide will not be widened. Therefore, from the conventional point ofview, the refractive index of the proton exchange layer should not varyat all. However, in an experiment by the inventors, the refractive indexincreased again by the annealing at 300° C. for 1 minute. Moreover, aphenomenon was observed where the refractive index decreased again withthe passage of time after this annealing.

[0139] The present invention makes it possible to mitigate the straingenerated in the proton exchange layer due to a heat treatment at arelatively high temperature, and thus to prevent the temporal variationof the optical wavelength conversion element.

[0140] Hereinafter, examples will be described with reference to theaccompanying drawings.

EXAMPLE 1

[0141] Referring to FIG. 7, Example 1 of the present invention will bedescribed.

[0142] In an optical wavelength conversion element of the presentexample, an optical waveguide of a stable proton exchange layer isformed in an LiTaO₃ substrate 1, and a plurality of domain invertedlayers 3 are periodically arranged along the optical waveguide. Bymaking a fundamental wave P1 incident upon an input end of the opticalwaveguide, a harmonic wave P2 is emitted from an output end thereof. Thelength of the optical wavelength conversion element (length of theoptical waveguide) is 9 mm in the present example. Moreover, in order toallow for operation at a wavelength of 850 nm, the length of a pitch ofthe domain inverted layers 3 is set to 3.7 μm.

[0143] Hereinafter, referring to FIGS. 8A to 8E, a production method ofthe optical wavelength conversion element will be described.

[0144] First, as shown in FIG. 8A, a Ta film is deposited so as to coverthe principal surface of the LiTaO₃ substrate 1, after which ordinaryphotolithography and dry etching techniques are used to pattern the Tafilm (thickness: about 200 to 300 nm) into a striped pattern, therebyforming the Ta mask 6. The Ta mask 6 used in the present example has apattern where strips each 1.2 μm wide and 10 mm long are arranged so asto be equally spaced apart from one another, and the arrangement pitchof the strips is 3.7 μm. A proton exchange process is performed for theLiTaO₃ substrate 1 whose principal surface is covered by the Ta mask 6.The proton exchange process is performed by immersing the surface of thesubstrate 1 for 14 minutes in a pyrophosphoric acid heated to 230° C.Thus, 0.5 μm thick proton exchange layers 7 are formed in portions ofthe LiTaO₃ substrate 1 which are not covered by the Ta mask. Then, theTa mask is removed by etching for 2 minutes using a mixture containingHF:HNF₃ at 1:1.

[0145] Next, as shown in FIG. 8B, a domain inverted layer is formed ineach of the proton exchange layers 7 by performing a heat treatment at atemperature of 550° C. for 15 seconds. In the heat treatment, thetemperature rise rate is 50 to 80° C./sec and the cooling rate is 1 to50° C./sec. In portions of the LiTaO₃ substrate 1 where the protonexchange has been performed, the amount (concentration) of Li is reducedas compared to that in other portions thereof where the proton exchangehas not been performed. Therefore, the Curie temperature of the protonexchange layer 7 decreases as compared to that in other portions,whereby the domain inverted layer 3 can be formed partially in theproton exchange layer by a heat treatment at a temperature of 550° C.This heat treatment allows for formation of the domain inverted layers 3having a periodic pattern reflecting the pattern of the Ta mask 6.

[0146] Next, the Ta mask (not shown) used for forming the opticalwaveguide is formed. The Ta mask is obtained by forming slit-shapedopenings (width: 4 μm, length: 12 mm) in a Ta film (thickness: about 200to 300 nm) deposited on the substrate 1. The openings define the planarlayout of the waveguide. It is needless to say that the shape of thewaveguide is not limited to the linear shape. The pattern of the Ta maskis determined depending upon the shape of a waveguide to be formed. Byperforming a proton exchange process at 260° C. for 16 minutes withrespect to the LiTaO₃ substrate 1 covered by the Ta mask, alinearly-extending proton exchange layer (thickness: 0.5 μm, width: 5μm, length 10 mm) 5 is formed in a region of the LiTaO₃ substrate 1under an opening of the Ta mask, as shown in FIG. 8C. Thelinearly-extending proton exchange layer 5 will eventually function as awaveguide. Then, the Ta mask is removed by etching for 2 minutes using amixture containing HF:HNF₃ at 1:1.

[0147] Next, an infrared heating equipment is used to perform annealingat 420° C. for 1 minute. By this annealing, non-linearity of the protonexchange layer 5 is restored, while an altered layer 8 b where therefractive index is increased by about 0.03 is formed, as shown in FIG.8D. As described above, this annealing serves to allow Li and proton tobe diffused in the substrate 1 and to reduce the proton exchangeconcentration of the proton exchange layer 5. Thereafter, a 300 nm thickSiO₂ layer (not shown), which functions as a protective layer, isdeposited on the principal surface of the substrate 1.

[0148] Next, after the surface of the substrate 1 perpendicular to thealtered layer 8 b is optically polished so as to form an incidentportion and an emitting portion of the optical wavelength conversionelement, an antireflection (AR) coating 15 is formed on the polishedsurface of the incident portion and the emitting portion, as shown inFIG. 8E.

[0149] Next, low-temperature annealing is performed for preventingtemporal variation. In the specification of the present application,“low-temperature annealing” means a heat treatment performed at atemperature which does not substantially reduce the proton concentrationin the proton exchange layer. For example, in the case of the LiTaO₃substrate, “low-temperature annealing” means a heat treatment performedat a temperature of about 130° C. or lower. In the present example, aheat treatment is performed at 60° C. for 40 hours under an airatmosphere using an oven. By such low-temperature annealing, a stableproton exchange layer 8 a is formed. The stable proton exchange layer 8a forms the optical waveguide.

[0150] Referring to FIG. 9, the flow of the above-described productionsteps will be described.

[0151] After a step of forming the domain inverted layers in thesubstrate (step S10), an optical waveguide formation step (S20) isperformed. The optical waveguide formation step (S20) is generallydivided into step S21, step S22 and step S23. The mask pattern is formedat step S21; the proton exchange process is performed at step S22; andhigh-temperature annealing is performed at step S23. Then, a protectivefilm formation step (step S30), an end face polishing step (step S40),an AR coating step (step S50) are performed. Since the wavelengthconversion element, as thus formed, will have some temporal variation,low-temperature annealing is performed at step S60 so as to form astable proton exchange layer.

[0152]FIG. 10 illustrates the relationship with the annealing time incases where low-temperature annealing is performed respectively at 60°C. and 120° C. The amount of phase-matched wavelength shift becomessubstantially constant after a few hours in the case of annealing at120° C., but it takes some ten hours to become substantially constant inthe case of annealing at 60° C.

[0153] It can be seen from FIG. 10 that a steady state is achieved in ashorter annealing time as the temperature of the low-temperatureannealing is higher. Moreover, as the annealing temperature is lower,the amount of phase-matched wavelength shift when achieving the steadystate indicates a value closer to zero. Thus, if the temperature of thelow-temperature annealing is increased, a period of time required forthe shift amount to return to zero becomes shorter, but, on the otherhand, a relatively great strain will remain.

[0154]FIG. 11 illustrates the relationship between the amount ofphase-matched wavelength shift when a steady state is achieved and thetemperature of low-temperature annealing. It can be seen from FIG. 11that the phase-matched wavelength becomes stable in the condition wherebeing shifted by about 0.5 nm when annealing is performed at 120° C. Ifannealing is performed at 150° C. or higher, the amount of phase-matchedwavelength shift after stabilization is 0.8 nm or more. If aphase-matched wavelength shift of such a magnitude remains, long-termuse of the optical wavelength conversion element becomes difficult. Ifthe tolerance range of the phase-matched wavelength shift is set to be0.5 nm or less, the amount of shift cannot be reduced to fall within thetolerance range even if annealing is performed at a temperatureexceeding 120° C. When the tolerance range of the phase-matchedwavelength shift is extended, the conversion efficiency is reduced. Whenthe amount of the phase-matched wavelength shift exceeds 0.5 nm, only anoutput about ¼ of that obtainable when the shift amount is zero isobtained. If low-temperature annealing is performed at 60° C., theannealing time is longer, but the shift amount can be reduced to be 0.1nm or less, whereby the problem of the reduced conversion efficiency iseliminated. It is preferable to suppress the amount of shift in thephase-matched wavelength to be about 0.2 nm or less.

[0155] According to the present example, the respective refractiveindices of the domain non-inverted layer 4 and the domain invertedlayers 3 in the optical waveguide 2 have no temporal variation, and thepropagation loss as light is being guided is small. When laser light(wavelength: 850 nm) from a semiconductor laser was made incident uponthe incident portion as the fundamental wave P1 so as to propagatethrough the optical waveguide, the light propagated in a single mode,and the harmonic wave P2 having a wavelength of 425 nm was taken out ofthe substrate through the emitting portion. The harmonic wave P2 waseffectively obtained with a small propagation loss of 1 dB/cm in theoptical waveguide 2. For an input of a fundamental wave of 27 mW, aharmonic wave (wavelength: 425 nm) of 1.2 mW was obtained. In this case,the conversion efficiency is 4.5%.

[0156]FIG. 12 illustrates the relationship between the number of dayselapsed and the harmonic wave output. FIG. 13 illustrates therelationship between the number of days elapsed and the phase-matchedwavelength and, as well as the relationship between the number of dayselapsed and the refractive index variation.

[0157] It can be seen from these figures that the refractive indexvariation and the phase-matched wavelength become constant immediatelyafter production of the element. According to the production method ofthe optical wavelength conversion element of the present invention, itwas possible to realize an optical wavelength conversion element whichhas no refractive index variation with the passage of time and whichthus has a constant phase-matched wavelength. By combining this elementwith a semiconductor laser, it is possible to produce a stable shortwavelength laser. At a temperature of about 60° C., low-temperatureannealing for 40 hours or more is particularly effective.

EXAMPLE 2

[0158] Next, Example 2 of the present invention will be described.

[0159] First, a Ta film is deposited so as to cover the principalsurface of the LiTaO₃ substrate, after which ordinary photolithographyand dry etching techniques are used to pattern the Ta film (thickness:about 200 to 300 nm) into a striped pattern, thereby forming the Tamask. The Ta mask used in the present example has a pattern where stripseach 1.2 μm wide and 10 mm long are arranged so as to be equally spacedapart from one another, and the arrangement pitch of the strips is 3.6μm. A proton exchange process is performed for the LiTaO₃ substrate 1whose principal surface is covered by the Ta mask. The proton exchangeprocess is performed by immersing the surface of the substrate for 20minutes in a pyrophosphoric acid heated to 260° C. Thus, 0.5 μm thickproton exchange layers are formed in portions of the LiTaO₃ substrate 1which are not covered by the Ta mask. Then, the Ta mask is removed byetching for 2 minutes using a mixture containing HF:HNF₃ at 1:1.

[0160] Next, a domain inverted layer is formed in each of the protonexchange layers 7 by performing a heat treatment at a temperature of550° C. for 15 seconds. In the heat treatment, the temperature rise rateis 50° C./sec and the cooling rate is 10° C./sec. This heat treatmentallows for formation of the domain inverted layers having a periodicpattern reflecting the periodic pattern of the Ta mask.

[0161] Referring to FIG. 14, the flow of the steps following theabove-described steps will be described.

[0162] First, a proton exchange process is performed for the surface ofthe substrate on which the domain inverted layers are arranged so as toform an optical waveguide (step S100). A Ta film, in which slits each 4μm wide and 12 mm long are formed, is used as a mask for forming theoptical waveguide.

[0163] Next, proton exchange is performed at 260° C. for 16 minutes in apyrophosphoric acid (step S110), after which the Ta mask is removed.After covering the principal surface of the substrate with an SiO₂ filmhaving a thickness of 300 nm, low-temperature annealing (step S120) isperformed so as to complete the formation of the optical waveguide. Forthe low-temperature annealing, a heat treatment in air at 120° C. wasperformed for 200 hours in order to prevent the refractive index fromincreasing. By this low-temperature annealing, a stable proton exchangelayer is formed.

[0164] Through the above-described steps, the domain inverted layers andthe optical waveguide are formed in the substrate. When the thickness ofthe domain inverted layer is set to 2.2 μm, in order to effectivelyperform wavelength conversion, the thickness d of the optical waveguideis set to be thinner than the thickness of the domain inverted layer,e.g., 1.8 μm. In order to allow for operation at a wavelength of 840 nm,the pitch of the domain inverted layers is set to 3.6 μm.

[0165] According to the above-described production method, therespective refractive indices of the domain non-inverted layer and thedomain inverted layers have no temporal variation, and the propagationloss of light is small. The surface perpendicular to the opticalwaveguide was optically polished so as to form an incident portion andan emitting portion. Thus, an optical wavelength conversion element canbe produced. Moreover, the length of the element is 9 mm.

[0166] When semiconductor laser light (wavelength: 840 nm) as thefundamental wave P1 was made incident upon the incident portion of thewaveguide, the harmonic wave P2 having a wavelength of 420 nm was takenout of the substrate through the emitting portion. A harmonic wave(wavelength: 420 nm) having an output of 10 mW was obtained for an inputof a fundamental wave having an output of 80 mW. In this case, theconversion efficiency is 12%. The harmonic wave output was very stablewith no optical damage or no temporal variation. When a high-temperatureannealing step is not performed in the course of the process, as in thisexample, the temporal variation can be prevented.

EXAMPLE 3

[0167] Next, as Example 3 of the present invention, a case of using anLiNbO₃ substrate (thickness: 0.4 to 0.5 mm) will be described.

[0168] First, ordinary photolithography and dry etching techniques areused to form a Ta electrode (first Ta electrode) having a patternsimilar to the pattern of the Ta mask used in the above-describedexamples on the principal surface of the LiNbO₃ substrate.

[0169] Then, a Ta film (second Ta electrode) is deposited on the entirereverse surface of the substrate. The first Ta electrode formed on theprincipal surface of the substrate and the second Ta electrode formed onthe reverse surface of the substrate form an electrode structure forapplying an electric field across the substrate.

[0170] Next, a voltage (e.g., 10 kilovolts) is applied between the firstTa electrode and the second Ta electrode so as to form an electric fieldin the LiNbO₃ substrate. By the application of an electric field, adomain inverted layer is formed so as to extend from a portion of thesurface of the substrate being in contact with the first Ta electrode tothe reverse surface of the substrate.

[0171] Next, etching is performed for 2 minutes using a mixturecontaining HF:HNF₃ at 1:1 so as to remove the Ta electrode. Then, a Tamask having slit-shaped openings (width: 4 μm, length: 12 mm) is formedon the substrate, after which a proton exchange process (230° C., 10minutes) using a pyrophosphoric acid is performed so as to form anoptical waveguide. After removing the Ta mask, annealing at 420° C. for2 minutes is performed using infrared heating equipment. By thisannealing, non-linearity in the optical waveguide is restored, but analtered layer is formed where the refractive index is increased by about0.02.

[0172] Then, a 300 nm thick SiO₂ film, which functions as a protectivefilm, is deposited on the substrate. Next, in order to mitigate thestrain which causes the refractive index to increase, annealing in airat 100° C. for 20 hours (first stage low-temperature annealing) isperformed, which is followed by annealing at 60° C. for 10 hours (secondstage low-temperature annealing). Thus, two stages of low-temperatureannealing are performed in the present example. The low-temperatureannealing is performed in separate two stages in order to reduce thetotal amount of time required for the low-temperature annealing. Byannealing at 100° C., the strain is mitigated more quickly than inannealing at 60° C., but some strain remains which corresponds to theamount of the phase-matched wavelength shift at 100° C. as shown in FIG.11. Therefore, low-temperature annealing at 60° C. is additionallyperformed so as to completely eliminate the strain. This 2-stageannealing makes it possible to quickly and completely form the “stableproton exchange layer” which is unlikely to generate strain.

[0173] The thickness d of the optical waveguide formed by the steps asdescribed above is 1.8 μm. The arrangement pitch of the domain invertedlayers is 3 μm, and it operates at a wavelength of 840 nm. The surfaceperpendicular to the optical waveguide is optically polished so as toform the incident portion and the emitting portion. Thus, the opticalwavelength conversion element can be produced. Moreover, the length ofthe element is 10 mm. When semiconductor laser light (wavelength: 840nm) as the fundamental wave P1 was guided from the incident portion, theharmonic wave P2 having a wavelength of 420 nm was taken out of thesubstrate through the emitting portion. A harmonic wave (wavelength: 420nm) of 13 mW was obtained for an input of a fundamental wave of 80 mW.The harmonic wave output was very stable with no temporal variation.

[0174] Although two different low-temperature annealings at differenttemperatures (2-stage annealing) were performed in this example, it isalso applicable to perform low-temperature annealing where thetemperature is gradually lowered, for example, from 100° C. to 60° C. in30 hours.

EXAMPLE 4

[0175] Next, referring to FIGS. 15A to 15C, Example 4 of the presentinvention will be described.

[0176] First, as shown in FIG. 15A, a mixture film (LiNb_(0.5)Ta_(0.5)O₃film) 16′ of LiNbO₃ and LiTaO₃ is grown on the LiTaO₃ substrate 1 by aliquid phase epitaxial growth method. At this point of time, the growthtemperature exceeds 1000° C., and some strain remains at the interfacebetween the mixture film 16 and the LiTaO₃ substrate 1. Next, as shownin FIG. 15B, a resist mask 17 is formed on the mixture film 161 using anordinary photolithography technique. Next, as shown in FIG. 15C, aportion of the mixture film 16 which is not covered with the resist mask17 is removed by ion beam etching so as to leave the optical waveguide16 having a width of, for example, 4 μm.

[0177] After a 300 nm thick SiO₂ is deposited on the substrate 1 by avapor deposition method, low-temperature annealing is performed in orderto mitigate an increase in the refractive index. This annealing includesa first stage low-temperature annealing performed at 100° C. for 30hours and a subsequent low-temperature annealing performed at 70° C. for60 hours. By this low-temperature annealing, a stable optical waveguide16 with no refractive index variation is obtained.

[0178] The thickness d of the optical waveguide formed by theabove-described steps is 1.8 μm. Moreover, the length of the element is9 mm. The surface perpendicular to the optical waveguide was opticallypolished so as to form the incident portion and the emitting portion.When semiconductor laser light (wavelength: 840 nm) was guided from theincident portion, the waveguide loss was very small. It was very stablewith the temporal variation of the refractive index being less than themeasuring limit. The material of the mixture film is not limited toLiNb_(0.5)Ta_(0.5)O₃, but may also be LiNb_(x)Ta_(1−x)O₃ (0<x<1) or anyother optical material.

EXAMPLE 5

[0179] Next, Example 5 of the present invention will be described.

[0180] Referring to FIG. 16, the outline of the process flow of thepresent example will be described.

[0181] First, an optical waveguide formation step is performed. Theoptical waveguide formation step is generally divided into step S200,step S210 and step S220. The mask pattern is formed at step S200; theproton exchange process is performed at step S210; and high-temperatureannealing is performed at step S220. Then, an electrode formation step(step S230), a low-temperature annealing step (step S240), an end facepolishing step (step S250) and an AR coating step (step S260) areperformed.

[0182] Hereinafter, details of the process will be described.

[0183] First, ordinary photo process and dry etching are used to patternTa into slits. Next, proton exchange is performed at 30° C. for 10minutes for the LiTaO₃ substrate 1, on which the pattern of Ta has beenformed, so as to form a 0.5 μm thick proton exchange layer directlyunder the slit. Next, Ta is removed by etching for 2 minutes using amixture containing HF:HNF₃ at 1:1. A diffusion furnace is used toperform annealing (first annealing) at 400° C. for 1 hour, and analtered layer is formed where the refractive index is increased by about0.01. Next, as the electrode formation step, 300 nm of SiO₂ was added byvapor deposition. After Al was deposited into a striped shape as anelectrode mask, patterning was performed. Next, low-temperatureannealing was performed in order to mitigate an increase in refractiveindex. Annealing was performed in air at 70° C. for 10 hours. Thus, astable proton exchange layer is formed. Herein, the second annealing wasperformed at a temperature lower than that in the first annealing by330° C. Lowering it by 200° C. or more is effective because the straincan be greatly mitigated thereby. Finally, polishing and AR coating wereperformed.

[0184] By the steps as described above, an optical waveguide with anelectrode was produced. This functions as an optical modulator. Thethickness of the optical waveguide is 8 μm. The surface perpendicular tothe optical waveguide was optically polished so as to form the incidentportion and the emitting portion. Thus, an optical element can beproduced. Moreover, the length of the element is 9 mm. When a modulationsignal is applied to the electrode so as to guide semiconductor laserlight (wavelength: 1.56 μm) as a fundamental wave from the incidentportion, modulated light was taken out through the emitting portion.There was no temporal variation, and the bias voltage remained stablefor more than 2000 hours.

[0185] Although the present invention has been described in respect ofan optical wavelength conversion element and an optical modulator as anexample of an optical element in the above-described examples, thepresent invention is not limited thereto, but may also be applied to aflat device such as a Fresnel lens or a hologram. Temporal variation inrefractive index associated with the proton exchange process can beprevented while deterioration of characteristics can be suppressed.

EXAMPLE 6

[0186] Next, referring to FIG. 17, Example 6 of the present inventionwill be described. The present example is a short wavelength lightsource including a semiconductor laser and an optical wavelengthconversion element.

[0187] As shown in FIG. 17, the pumped light P1 a emitted from thesemiconductor laser 20 is collected by the lens 30 so as to excite theYAG 21 as a solid-state laser crystal.

[0188] The total reflection mirror 22 for 947 nm is formed on the YAG21, whereby laser oscillation occurs at a wavelength of 947 nm so as toradiate the fundamental wave P1. On the other hand, the total reflectionmirror 23 for the fundamental wave P1 is formed on the emitting side ofthe optical wavelength conversion element 25, whereby laser oscillationoccurs therebetween. The fundamental wave P1 is collected by a lens 31,and the fundamental wave P1 is converted to the harmonic wave P2 by theoptical wavelength conversion element 25. In this example, the opticalwaveguide 2 produced in the LiTaO₃ substrate 1 by utilizing protonexchange is used as an optical wavelength conversion element havingperiodic domain inverted structures where a periodic structure isformed.

[0189] In FIG. 17, reference numeral 1 denotes an LiTaO₃ substrate of aZ plate; 2 denotes a formed optical waveguide; 3 denotes a domaininverted layer; 10 denotes an incident portion for the fundamental waveP1; and 12 denotes an emitting portion for the harmonic wave P2. Thefundamental wave P1 which has entered the optical waveguide 2 isconverted to the harmonic wave P2 by the domain inverted layer 3 whichhas a length of the phase-matched length L, and the harmonic wave poweris then increased by the domain non-inverted layer 4 which also has thelength of L.

[0190] In this manner, the harmonic wave P2 whose power has beenincreased in the optical waveguide 2 is radiated from the emittingportion 12. The radiated harmonic wave P2 is collimated by the a lens32.

[0191] Moreover, an electrode 14 is formed in the optical wavelengthconversion element 25 via a protective film 13. Next, the productionmethod of the optical wavelength conversion element 25 will be brieflydescribed referring to the figures.

[0192] First, as shown in FIG. 18A, ordinary photolithography and dryetching techniques are used to form a Ta electrode (first Ta electrode)6 having a pattern similar to the pattern of the Ta mask used in theabove-described respective examples on the principal surface of the 0.3mm thick LiNbO₃ substrate 1.

[0193] Then, a Ta film (second Ta electrode) 6 b is deposited on theentire reverse surface of the substrate 1. The first Ta electrode 6formed on the principal surface of the substrate 1 and the second Taelectrode 6 b formed on the reverse surface of the substrate 1 form anelectrode structure for applying an electric field across the substrate1.

[0194] Next, a voltage (e.g., 10 kilovolts) is applied between the firstTa electrode 6 and the second Ta electrode 6 b so as to form an electricfield in the LiNbO₃ substrate 1. By the application of an electricfield, a domain inverted layer 3 is formed so as to extend from aportion of the surface of the substrate 1 in contact with the first Taelectrode 6 to the reverse surface of the substrate 1, as shown in FIG.18B. The length L of the domain inverted layer 3 along the direction inwhich light propagates is 2.5 μm. Then, etching is performed for 20minutes using a mixture containing HF:HNF₃ at 1:1 so as to remove the Taelectrodes 6 and 6 b.

[0195] Then, a Ta mask (not shown) having slit-shaped openings (width: 4μm, length: 12 mm) is formed on the substrate 1, after which a protonexchange process (260° C., 40 minutes) using a pyrophosphoric acid isperformed so as to form the optical waveguide 2, as shown in FIG. 18C.The Ta mask has slits (width: 6 μm, length: 10 mm), and the slits definethe planar layout of the optical waveguide 2. After removing the Tamask, annealing for 5 hours at 460° C. is performed using infraredheating equipment. By this annealing, the optical waveguide for whichproton exchange has been performed restores its non-linearity, and therefractive index at the portion increases by about 0.002. Lightpropagates along the optical waveguide 2 having a high refractive index.The thickness d of the optical waveguide 2 is 50 μm, and the widththereof is 70 μm. The arrangement pitch of the domain inverted layers 3along the direction in which the waveguide 2 extends is 5 μm, and theoptical wavelength conversion element operates for a fundamental wavehaving a wavelength of 947 nm.

[0196] Next, as shown in FIG. 18D, after a protective film (thickness:300 to 400 nm) 13 made of SiO₂ is formed on the substrate 1, an Al film(thickness: 200 nm) is formed on the protective layer 13 by vapordeposition. The Al film is patterned by photolithography technique so asto form the Al electrode 14. The Al electrode 14 is used for modulatingthe intensity of output light.

[0197] The surface perpendicular to the direction in which the opticalwaveguide 2 extends is optically polished so as to form the incidentportion 10 and the emitting portion 12 as shown in FIG. 17. Moreover, anantireflection coating for the fundamental wave P1 is applied onto theincident portion 10. A reflective coating (99%) for the fundamental waveP1 and an antireflection coating for the harmonic wave P2 are appliedonto the emitting portion 12.

[0198] In this way, the optical wavelength conversion element 25(element length: 10 mm) as shown in FIG. 17 can be produced.

[0199] In FIG. 17, when light having a wavelength of 947 nm as thefundamental wave P1 was guided from the incident portion 10, itpropagated in a single mode, and the harmonic wave P2 having awavelength of 473 nm was taken out of the substrate through the emittingportion 12. The propagation loss in the optical waveguide 2 was as smallas 0.1 dB/cm, thus improving the performance of the cavity, increasingthe power concentration of the fundamental wave P1, and generating theharmonic wave P2 at a high efficiency.

[0200] Possible causes for the reduced loss may include that a uniformoptical waveguide was formed by the phosphoric acid and that theconfinement in the waveguide was reduced. Moreover, due to the opticalwaveguide with the weak confinement, the harmonic wave concentration wasreduced, and the optical damage was considerably improved. This isbecause, an area 100 times larger with respect to that in a conventionaltechnique can tolerate a 100 times greater optical damage.

[0201]FIG. 19 illustrates the relationship between the optical waveguidethickness and the endurance power against optical damage. The endurancepower against optical damage is a power that indicates the highest blueharmonic wave which can be tolerated, i.e., the highest blue harmonicwave for which optical variation does not occur. It can be seen that,when the thickness of the optical waveguide is widened, the widththereof is also simultaneously widened due to diffusion, whereby theendurance power against optical damage is improved in relation to theoptical waveguide thickness being substantially squared. Since the powerrequired for laser radiation is at least 2 W, it is preferable that theoptical waveguide thickness is 40 μm or greater.

[0202] Moreover, if the cross-section of the waveguide is enlarged inthe case where the refractive index distribution in and in the vicinityof the waveguide varies in a stepped manner, a multi-mode propagationphenomenon occurs. In order to avoid this, a waveguide having a gradedtype refractive index distribution is formed in the present example.

[0203] When the output of the output light P1 a from the semiconductorlaser 20 was 10 W, a harmonic wave P3 having an output of 3 W wasobtained. In this case, the conversion efficiency is 30%. The tolerancerange of the optical wavelength conversion element against thewavelength variation is 0.4 nm. Even if the wavelength is shifted by 0.4nm, the oscillation wavelength of the solid state laser was constant,while the harmonic wave output was stable. By applying a voltage to theAl electrode 14 for modulation, the refractive index varies in and inthe vicinity of the waveguide, thereby shifting the phase-matchedwavelength of the optical wavelength conversion element. By utilizingthe phenomenon that the phase-matched wavelength is greatly shifted by avoltage application, it is possible to modulate the harmonic wave outputwith application of a relatively low voltage of about 100 V.

[0204] Thus, with the optical wavelength conversion element using theperiodic domain inverted structures used in the present example, it ispossible to easily modulate the harmonic wave output by applying avoltage, and a voltage required to be applied is thus low, providinghigh industrial applicability.

[0205] Thus, a modulator can be integrated, whereby it is possible toachieve smaller size, lighter weight and lower cost. Moreover, there isanother feature that LiTaO₃, which is a non-linear optical crystal usedin the present invention, can be obtained in a large crystal, whereby itis easy to mass produce the optical wavelength conversion element usingan optical IC process. Multi-mode propagation for a fundamental waveresults in an unstable harmonic wave output and is thus unpractical,whereas a single mode is effective. It is highly desirable to use anelement having periodic domain inverted structures as the opticalwavelength conversion element, as in this example, since this makes itpossible to improve efficiency and realize integration of the opticalmodulator, as well as allowing red and green laser light in addition toblue laser light to be taken out by varying the pitch. The opticalmodulator may also be separated.

[0206] Next, referring to FIG. 20, an example of a laser projectionapparatus of the present invention will be described. As shown in FIG.20, the blue laser light source shown in FIG. 17 was used as the lightsource for this laser projection apparatus. Reference numeral 45 denotesa laser light source having a wavelength in the 473 nm band which isblue color. The blue light is modulated by inputting a modulation signalto a modulation electrode. The blue laser light which has been modulatedis incident upon a deflector. Reference numeral 56 denotes a verticaldeflector, and 57 denotes a horizontal deflector, for both of which arotating polygon mirror is used. A brightness of 300 cd/m², a contrastratio of 100:1 and a horizontal resolution of 1000 TV were obtained fora screen size of 4 m×3 m using a screen 70 having a gain of 3. Thus, theresolution was considerably improved as compared to that in aconventional technique. As compared to a configuration using a gaslaser, other considerable improvements were also achieved such as aone-thousandth weight, a one-thousandth volume and a one-hundredth powerconsumption. The small size and the low power consumption of the laserlight source and the integration of the optical modulator greatlycontribute to these achievements. That is, this results from that theconfiguration using a semiconductor laser and an optical wavelengthconversion element can be subminiaturized, and that the efficiency ofconversion from an electrical power is higher than that of a gas laserby about two orders of magnitude. Particularly, it is significantlyeffective to use an element having periodic domain inverted structuresas an optical wavelength conversion element, whereby efficiency can beimproved while the optical modulator can be integrated. Although thescreen is irradiated with laser light from the reverse side thereof inthe present example, it is also applicable to radiate it from the frontside thereof.

[0207] Next, referring to FIG. 21, another example of a laser lightsource of the present invention will be described.

[0208] As shown in FIG. 21, the fundamental wave P1 emitted from thesemiconductor laser 20 is guided to the optical wavelength conversionelement 25 via the lens 30, a half-wave plate 37 and a collective lens31, and is converted to the harmonic wave P2. That is, in this example,blue light is obtained without using a solid state laser. The structureof the optical wavelength conversion element 25 is substantially thesame as that in Example 1. The present example also uses an LiTaO₃substrate and an optical wavelength conversion element of the opticalwaveguide type. Moreover, for performing optical modulation, theelectrode 14 and the protective film 13 are formed. However, the presentexample does not employ the cavity structure.

[0209]FIG. 22 illustrates an internal structure of the semiconductorlaser 20. The semiconductor laser 20 is composed of a distributedfeedback type (hereinafter, abbreviated as DBR) semiconductor laser 20 aand a semiconductor laser amplifier 20 b. The DBR semiconductor laser 20a is provided with a DBR section 27 using a grating, and thus stablyoscillates at a constant wavelength. A stabilized fundamental wave P0emitted from the DBR semiconductor laser 20 a is guided to thesemiconductor laser amplifier 20 b by a lens 30 a. The power isamplified by an active layer 26 b of the semiconductor laser amplifier20 b so as to provide a stable fundamental wave P1. By incorporatingthis into the optical wavelength conversion element 25, the conversionefficiency and the harmonic wave output are considerably improved. Thepitch of domain inversion is 3 μm, and the optical waveguide length is 7mm. In this example, the oscillation wavelength of the semiconductorlaser was 960 nm, the wavelength of the generated harmonic wave P2 was480 nm, and the color was blue. The conversion efficiency is 10% for aninput of 10 W. There was no optical damage, and the harmonic wave outputwas very stable. A DBR semiconductor laser has a stable oscillationwavelength and is favorable in stabilizing the harmonic wave output.

[0210] Next, an RF superimposition (radio frequency superimposition) wasperformed for this DBR semiconductor laser. A pulse train was opticallyoutput from the semiconductor laser by applying a sine-shaped electricwaveform of 800 MHz to the DBR semiconductor and utilizing therelaxation oscillation. When the RF superimposition is thus performedfor the DBR semiconductor laser, the peak output of the fundamental waveis considerably improved while keeping the oscillation wavelengthconstant. For a fundamental wave with an average output of 10 W, aharmonic wave of 5 W was obtained with a conversion efficiency of 50%.The conversion efficiency was improved by 5-fold as compared to the casewhen the RF superimposition is not performed.

[0211] Although the DBR semiconductor laser and the semiconductor laseramplifier were separated from each other in the present example, furtherminiaturization can be achieved if they are integrated.

[0212] Next, referring to FIG. 23, still another example of the laserlight source of the present invention will be described. The fundamentalwave P1 from the semiconductor laser 20 is gently collected to theoptical wavelength conversion element 25 by the lens 30. In the presentexample, LiNbO₃ was used as a substrate in place of the LiTaO₃substrate. Moreover, the bulk type optical wavelength conversion element25 is used. The LiNbO₃ substrate 1 a has a feature of largenon-linearity. The peak power is improved by the RF driving of thesemiconductor laser 20, whereby the conversion efficiency of the opticalwavelength conversion element is considerably improved. The pitch of thedomain inverted layers 3 is 3.5 μm, and the length of the opticalwavelength conversion element 25 is 7 mm. In this example, the output ofthe harmonic wave P2 is stabilized by using the optical feedback method.The wavelength tolerance range of the optical wavelength conversionelement 25 is as narrow as about 0.1 nm. The fundamental wave P1 whichhas not been converted by the optical wavelength conversion element 25is collimated by the lens 32 and is reflected by a grating 36 so as toreturn to the semiconductor laser 20. Thus, the oscillation wavelengthof the semiconductor laser 20 is locked at the reflection wavelength ofthe grating 36. In order to adjust the oscillation wavelength to thephase-matched wavelength of the optical wavelength conversion element25, the angle of the grating 36 can be varied.

[0213] On the other hand, the harmonic wave P2 is reflected by adichroic mirror 35 so as to be taken out in a different direction. Inthis example, the oscillation wavelength of the semiconductor laser was980 nm, and the harmonic wave P2 taken out was blue light at 490 nm. Atthis time, an electric waveform having an RF frequency of 810 MHz and anoutput of 5 W was applied. Moreover, a harmonic wave of 3 W was obtainedfor an average output of the fundamental wave being 15 W. There was nooptical damage and the harmonic wave output was very stable. The opticaldamage is not present because the fundamental wave is collected only toabout 100 μm, and the harmonic wave is accordingly not so large in termsof concentration.

[0214] Although a wavelength is locked by optical feedback using agrating in the present example, the present invention is not limitedthereto, but it is also applicable, for example, to achieve opticalfeedback by using a filter to select a wavelength. Moreover, if a laserprojection apparatus is formed using the laser light source of thepresent example, it is possible to achieve smaller size, lighter weightand lower cost. Furthermore, according to the present example, aharmonic wave can also be modulated by directly modulating thesemiconductor laser, whereby the configuration becomes simple, and it ispossible to reduce the cost.

[0215] Next, referring to FIG. 24, another example of a laser lightsource of the present invention will be described. The cross section ofthe optical wavelength conversion element (bulk type) 25 is shown inFIG. 24.

[0216] The pumped light P1 a emitted from the semiconductor laser 20having a wavelength of 806 nm is incident upon a fiber 40 and propagatesthrough the fiber 40. The pumped light P1 a emitted from the fiber 40enters the optical wavelength conversion element 25. The material of theoptical wavelength conversion element 25 is an LiTaO₃ substrate 1 b intowhich Nd, being a rare earth element, is doped, and the domain invertedstructures are formed with a pitch of 5.1 μm. The doping amount of Nd is1 mol %. Reference numeral 22 denotes a total reflection mirror whichtotally reflects 99% of light having a wavelength of 947 nm buttransmits light in the 800 nm band. Reference numeral 23 also denotes atotal reflection mirror but which totally reflects 99% of light having awavelength of 947 nm and transmits light in the 470 nm band. Moreover,the total reflection mirror section is processed to be a sphericalshape. That is, it serves as a spherical mirror. The optical wavelengthconversion element 25 oscillates at a wavelength of 947 nm as excited bythe semiconductor laser 20, and the light is converted to the harmonicwave P2 by the domain inverted structures of the domain inverted layers3 so as to be emitted out. A harmonic wave of 2 W was obtained for thepumped light P1 of 20 W. Moreover, temperature stabilization is providedby a Peltier element so that the temperature of the optical wavelengthconversion element does not vary considerably. The conversion section ofthe laser light source according to this example has a length of 10 mm,and it can be made very compact by doping a rare earth element into theoptical wavelength conversion element and designing it so that thepumped light propagates through a fiber. Moreover, it is possible toprevent temperature variation by remotely disposing the opticalwavelength conversion element away from the heat generated by thesemiconductor laser.

[0217] Furthermore, by changing the coating on the total reflectionmirrors 22 and 23 for reflection of the 1060 nm band, and changing thepitch of the domain inverted layers 3 for 1060 nm, oscillation wasachieved at 1060 nm, whereby green laser light (wavelength: 530 nm) wasobtained as the harmonic wave P2. Moreover, by changing the coating onthe total reflection mirrors 22 and 23 for reflection of the 1300 nmband, and changing the pitch of the domain inverted layers 3 for 1300nm, oscillation was achieved at 1300 nm, whereby red laser light(wavelength: 650 nm) was obtained as the harmonic wave P2. With thisconfiguration, primary color laser light, i.e., blue, green and redlight, can be easily obtained. Next, FIG. 25 illustrates anotherconfiguration where the solid state laser crystal and the opticalwavelength conversion element are separated from each other. Nd:YVO₄ asthe solid state laser crystal 21 was attached to the output side of thefiber. The domain inverted structures are periodically formed in theoptical wavelength conversion element 25 of the LiTaO₃ substrate 1. Bluelaser light of 2 W was stably obtained also by the laser light source ofthis configuration.

[0218] Still another example of the present invention will be describedreferring to the figures. FIG. 26 illustrates a configuration of a laserlight source according to the present example. The pumped light P1 aemitted from the semiconductor laser 20 having a wavelength of 806 nm isconverted to the fundamental wave P1 by the solid state laser crystal21, is incident upon the fiber 40, and propagates through the fiber 40.The fiber 40 is a single mode fiber. The fundamental wave P1 emittedfrom the fiber 40 enters the optical wavelength conversion element 25.In this example, the optical waveguide 2 which is produced in the LiTaO₃substrate 1 utilizing proton exchange is used as the optical wavelengthconversion element 25 with periodic domain inverted structures. In thefigure, reference numeral 1 denotes an LiTaO₃ substrate of a Z plate; 2denotes a formed optical waveguide; 3 denotes a domain inverted layer;10 denotes an incident portion for the fundamental wave P1; and 12denotes an emitting portion for the harmonic wave P2. The fundamentalwave P1 which has entered the optical waveguide 2 is converted to theharmonic wave P2 by the domain inverted layers 3. Thus, the harmonicwave P2 having the power increased in the optical waveguide 2 isradiated out through the emitting portion 12. The radiated harmonic waveP2 is collimated by the lens 32.

[0219] Moreover, the electrode 14 is formed on the element via theprotective film 13. The harmonic wave P2 of 10 W was obtained for thepumped light P1 a of 30 W. The blue laser light was modulated at 30 MHzby applying a modulation signal to the electrode 14 formed on theoptical wavelength conversion element 25. The conversion section of thelaser light source according to this example has a length of 10 mm, andit can be made very compact by designing it so that the fundamental waveP1 propagates through a fiber. Moreover, it is possible to preventtemperature variation by remotely disposing the optical wavelengthconversion element away from the semiconductor laser.

[0220]FIG. 26 illustrates an example where a solid state laser crystalis not used.

[0221] A semiconductor laser of 980 nm, having an output of 10 W, isused. This is coupled to the optical wavelength conversion element 25through the fiber 40 so as to perform direct conversion. An output of 2W was obtained for a wavelength of 490 nm.

[0222] Next, referring to FIG. 27, a laser projection apparatus of thepresent invention will be described. Light sources of three colors,i.e., the blue laser light source, the green laser light source and thered laser light source of Example 5 were used as light sources.Reference numeral 45 denotes a blue laser light source in the 473 nmwavelength band. Reference numeral 46 denotes a green laser light sourcein the 530 nm wavelength band; and 47 denotes a red laser light sourcein the 650 nm wavelength band. A modulation electrode is attached toeach of the optical wavelength conversion elements. Each light sourceoutput is modulated by inputting a modulation signal to the modulationelectrode. The green laser light is combined with the blue laser lightby the a dichroic mirror 61. Moreover, the red laser light is combinedwith the other two colors by a dichroic mirror 62. Reference numeral 56denotes a vertical deflector, and 57 denotes a horizontal deflector,both of which use a rotating polygon mirror. A brightness of 2000 cd/m²,a contrast ratio of 100:1, a horizontal resolution of 1000 TV and avertical resolution of 1000 TV were obtained for a screen size of 2 m×1m using a screen 70 having a gain of 3. Thus, the laser projectionapparatus of the present invention is significantly effective inproviding a high brightness, a high resolution and an extremely lowpower consumption.

[0223] Although an optical wavelength conversion element of the domaininverted type is used in the present example, it is not limited thereto.Moreover, when a laser light source which is directly oscillated by asemiconductor laser is used for red color, the cost can be furtherreduced. Alternatively, the semiconductor laser direct oscillation typemay be used as the blue or green laser. The combination thereof may befreely determined.

[0224] Moreover, in the present example, the following features havebeen devised for safety. The laser is designed to turn off automaticallywhen the laser light scanning is terminated. Infrared laser light beingsub-semiconductor laser with a weak output is scanning around theprojected laser light, and it is designed so that the laser light isautomatically turned off when an object contacts the light. An infraredsemiconductor laser has a feature of a low cost and a long life.

[0225] Next, these will be described referring to FIG. 28. The threelaser light beams of the primary colors are scanned by the deflectorwithin a display area 71 of the screen 70. The laser light passes oversensors A and B located on the periphery of the display area 71. Outputsignals from the sensors A and B are always being monitored. On theother hand, the laser light from the infrared laser light source of aninfrared semiconductor laser is always scanned by a deflector 58 alongthe periphery of the screen 70. The reflected light enters a sensor C.That is, it is designed so that light reflected at any position alongthe periphery enters the sensor C.

[0226] Next, control will be described referring to FIG. 29. In FIG. 29,when a signal from either one of the sensors A and B does not enter acontrol circuit for a certain period of time, the main power of thelaser light source is turned off so that the blue, red and green laserlight sources are turned off. That is, by terminating the scanning, itis possible to prevent a certain position from being irradiated with thelaser light in a concentrated manner. Moreover, if the signal from thesensor C is discontinued even for a moment, the power of the laser lightsource is turned off by the control circuit. Thus, it is safe since ahuman, etc., never touches the short wavelength laser light having ahigh output. The safety of this laser projection apparatus is maintainedas described above.

[0227] Although the power of the laser light source is turned off in theexample, it is also applicable to block the optical path of the laser.Moreover, generation of short wavelength laser light may be terminatedby shifting the phase-matched wavelength of the optical wavelengthconversion element using a voltage or the like, or by varying theoscillation wavelength of the semiconductor laser as a fundamental wavelight source. This method allows for considerable reduction of theperiod of time required for a restart.

[0228] Next, referring to FIG. 30, an example of a three-dimensionallaser projection apparatus of the present invention will be described.

[0229] This is an apparatus which provides a stereoscopic view for aviewer. FIG. 30 illustrates a configuration of the laser projectionapparatus according to the present example. As shown in FIG. 30, byinserting a prism type optical path convertor 66 for three color laserlight, the laser light is split into two directions. The split laserlight beams are reflected by respective mirrors 64 and 65 and modulatedby modulators 5 a and 5 b, so as to be incident upon the screen 70. Animage viewed from the right direction and an image viewed from the leftdirection are respectively superimposed by the modulators 5 a and 5 b,and the light beams are incident upon the screen 70 from differentdirections, thereby being viewed stereoscopically. Moreover, an opticalpath 1 and an optical path 2 are switched with each other at regularintervals so that a human feels as if different images are coming fromtwo directions, thereby making the stereoscopical image even clearer. Asin this example, a stereoscopic image can be easily viewed withoutstereoscopic glasses.

[0230] A stereoscopic view can also be realized by splitting light intwo by a half mirror, or the like. Moreover, although a single lightsource is split in the above example, two laser light sources of thesame color may be used to irradiate the screen from differentdirections. In this case, only half the output is required for eachlight source.

[0231] Next, still another example of a laser projection apparatus ofthe present invention will be described.

[0232]FIG. 31 illustrates a configuration of the laser projectionapparatus according to the present example. An ultraviolet laser lightsource based on the optical wavelength conversion element is used as alight source. By irradiating the screen 70 on which a fluorescentsubstance is applied with the light, RGB light, i.e., red, green andblue light, is emitted. In the configuration of the laser light source,650 nm red laser light directly oscillated by a semiconductor laser wasmade to have half the wavelength, i.e., 325 nm, by an optical wavelengthconversion element of LiTaO₃. The optical wavelength conversion elementis of the bulk type in which the domain inverted structures are formed.Reference numeral 48 denotes the laser light source. Herein, anultraviolet modulation signal is obtained by directly modulating redsemiconductor laser. The modulated ultraviolet laser light enters adeflector. Reference numeral 56 denotes a vertical deflector, and 57denotes a horizontal deflector, both of which use a rotating polygonmirror. The screen 70 has fluorescent substances applied thereonrespectively for generating red, green and blue light, and thusgenerates fluorescent light. A brightness of 300 cd/m², a contrast ratioof 100:1 and a horizontal resolution of 600 TV were obtained for ascreen size of 1 m×0.5 m. As in this example, it is possible to generatethe primary colors, i.e., red, green and blue, with a single laser lightsource, whereby it is possible to realize smaller size and lower cost.It is also favorable that the dichroic mirror for combining waves can beeliminated.

[0233] Next, referring to FIG. 32, a laser projection apparatus of thepresent invention will be described. As shown in FIG. 32, the blue laserlight source 45 based on the optical wavelength conversion element isused as a light source. Laser light emitted from the laser light source45 is collimated by the lens 30. A liquid crystal light bulb 68 isinserted in the collimated laser light. Light is spatially modulated byapplying a signal to the liquid crystal light bulb 68, enlarged by thelens 31 and projected onto the screen so that an image can be viewed.This can be done in multi-colors by using laser light sources of theprimary colors.

[0234] As compared to the conventional technique, the efficiency wasconsiderably improved and the power consumption was reduced. Moreover,it is also advantageous in that the amount of heat generated is small.

[0235] Next, referring to FIG. 32, a laser projection apparatus of thepresent invention will be described. The configuration in appearance isthe same as that in the example of the laser projection apparatusillustrated in FIG. 20. As a light source, the blue laser light sourceof FIG. 23 is used, and the laser light source used herein is RFsuperimposed. Moreover, the blue light is modulated by an input of amodulation signal in addition to the RF superimposition. The modulatedblue laser light is incident upon a deflector. A brightness of 200 cd/m²was obtained for a screen size of 2 m×1 m using a screen having a gainof 2. A speckle noise to be generated due to laser light interferencewas not observed on the screen. This results from the reduction ofcoherency of the laser light by the RF superimposition, and the RFsuperimposition significantly contributes to countermeasures for thespeckle noise. While the laser light source configuration of FIG. 23 isused in the present example, the RF superimposition is effective for alaser projection apparatus using a laser light source based on thedirect wavelength conversion of semiconductor laser. Moreover, a specklenoise can also be prevented in the case where red, green or blue laserlight is generated directly by semiconductor laser light. It is needlessto say that it is also effective for a color laser projection apparatus.

[0236] Although LiNbO₃ and LiTaO₃ are used as a non-linear opticalcrystal in the above-described example, it is also applicable to use aferroelectric substance such as KNbO₃ or KTP, an organic material suchas MNA, and other materials obtained by doping a rare earth element intothese materials. Moreover, as a rare earth element, Er or Tl is alsoprospective in addition to Nd which is used in the examples.Furthermore, although YAG is used as a solid state laser crystal, othercrystals such as YLF or YVO₄ are also effective. LiSAF and LiCAF arealso effective solid state laser crystals.

[0237] Next, referring to FIG. 33, an example where the laser lightsource of the present invention is applied to an optical disk apparatuswill be described.

[0238] The optical disk apparatus has the optical wavelength conversionelement 25, which includes the domain inverted structures, within anoptical pickup 104, whereby the laser light emitted from thesemiconductor laser 20 is passed to the optical wavelength conversionelement 25 within the optical pickup 104 via the fiber 40.

[0239] In addition to the optical wavelength conversion element 25, theoptical pickup 104 includes: a collimator lens 32 for convertihg aharmonic wave emitted from the optical wavelength conversion element 25to a collimated light; a polarization beam splitter 105 for transmittingthe collimated light to the optical disk; a collective lens 106 forcollecting the light onto the optical disk; and a detector 103 fordetecting reflected light from the optical disk. The polarization beamsplitter 105 selectively reflects the reflected light from the opticaldisk so as to pass it to the detector 103.

[0240] While the optical pickup 104 is driven by an actuator, thesemiconductor laser 20 is fixed in the optical disk apparatus. Theoptical pickup 104 can reliably receive, by the flexible optical fiber,laser light from the semiconductor laser 20 fixed in the optical diskapparatus.

[0241] Next, the operation will be described.

[0242] Light (pumped light) emitted from the semiconductor laser 20 isconverted to the fundamental wave P1 by the solid state laser 21, andradiated onto the optical wavelength conversion element 25. The opticalwavelength conversion element 25 has a configuration similar to that inthe above-described example and converts the fundamental wave P1 to theharmonic wave P2. The harmonic wave P2 is collimated by the collimatorlens 32, passes through the polarization beam splitter 105, and is thencollected onto the optical disk medium 102 via the collective lens 106.The reflected light from the optical disk medium 102 returns by the sameoptical path again, is reflected by the polarization beam splitter 105,and is detected by the detector 103.

[0243] Thus, a signal can be recorded on the optical disk medium, or asignal recorded thereon can be reproduced.

[0244] A quarter-wave plate 108 is inserted between the polarizationbeam splitter 105 and the collective lens 106 so as to rotate apolarization direction of a harmonic wave by 90 degrees on its way outand on its way back in.

[0245] When a semiconductor laser having an output of 1 W was used asthe semiconductor laser 20, a harmonic wave P2 of 200 mW was obtained.The wavelength of light emitted from the solid state laser 21 is 947 nm,and the wavelength of the harmonic wave is 473 nm.

[0246] By using high power laser light having an output of 200 mW, it ispossible to perform a recording operation at a speed 10 times fasterthan the recording speed achieved by an optical disk apparatus usingconventional 20 mW output light. The transfer rate was 60 Mbps.

[0247] Moreover, the semiconductor laser 20 which generates heat duringoperation is fixed in a housing of the optical disk apparatus, and isremote from the optical pickup. Thus, as a result of removal of thesemiconductor laser from the optical pickup, it is no longer necessaryto provide a special heat release structure for a semiconductor laser.It is thus possible to compose a subminiature and light weight opticalpickup. As a result, the optical pickup can be driven by an actuator ata high speed, whereby a fast recording operation at a high transfer ratecan be achieved.

[0248] Although the solid state laser is located on the side of thesemiconductor laser in the present example, it may also be located onthe side of the optical wavelength conversion element. Moreover, it isapplicable to convert light from the semiconductor laser as afundamental wave directly to a harmonic wave without using a solid statelaser.

[0249] The internal structure of the optical pickup 104 is not limitedto that of the present example. For example, by using a polarizationseparating hologram, it is possible to eliminate a lens and apolarization beam splitter. Thus, the optical pickup can be made furthersmaller.

INDUSTRIAL APPLICABILITY

[0250] As described above, in the optical wavelength conversion elementof the present invention, after an optical element is produced in anLiNb_(X)Ta_(1−X)O₃ (0≦X≦1) substrate, low-temperature annealing isperformed so as to repress an increase in refractive index generatedduring a heat treatment such as high-temperature annealing, and then, astable proton exchange layer is formed, whereby a stable optical elementcan be formed. Particularly, the present invention is indispensable forputting into practical use an optical wavelength conversion elementwhose phase-matched wavelength varies with refractive index variation.

[0251] Moreover, the 2-stage annealing with two different temperaturesis effective as the low-temperature annealing since it enables a stableproton exchange layer such that there is completely no temporalvariation to be restored quickly. It is further effective since thestrain can be greatly mitigated and a stable proton exchange layer canbe formed by performing second annealing at a temperature lower thanthat in first annealing by 200° C. It is further effective since thetemporal variation is 0.5 nm or less if the low-temperature annealing isperformed for at least 1 hour at a temperature of 120° C. or lower, andit is particularly effective if the temperature is 90° C. or less,whereby the phase-matched variation is small. If the temperature is 50°C. or lower, there will be a problem of an extremely long annealingtime. Therefore, the annealing needs to be performed at a temperaturethereabove.

[0252] Moreover, with the laser light source of the present invention,it is possible to stabilize the oscillation wavelength of thesemiconductor laser and to increase the fundamental wave output byinserting a semiconductor laser amplifier between a distributed feedbacktype semiconductor laser and an optical wavelength conversion element,while it is also possible to stably obtain the maximum harmonic waveoutput by using the highly efficient optical wavelength conversionelement having domain inverted layer structures.

[0253] Furthermore, with the laser light source of the presentinvention, the optical wavelength conversion element section can be madevery compact by designing it so that pumped light or a fundamental wavepropagates through a fiber. Furthermore, it is possible to remotelydispose the optical wavelength conversion element away from the heatgenerated by the semiconductor laser and thus to prevent temperaturevariation, whereby a high output semiconductor laser can be used.

[0254] Moreover, if periodic domain inverted structures are used as theoptical wavelength conversion element, in addition to a significantlyimproved conversion efficiency, modulation can be easily effected byapplying a low voltage, thereby presenting an industrial advantage.Thus, a modulator can be integrated, whereby it is possible to achievesmaller size, lighter weight and lower cost. Furthermore, by employingan optical waveguide with a weak confinement as the optical wavelengthconversion element, the concentration of a harmonic wave becomes small,whereby the optical damage is considerably improved. This is because, a100 times larger area with respect to that in a conventional techniquecan tolerate a 100 times greater optical damage. Furthermore, with thelaser light source of the present invention, it is possible to use ahigh output semiconductor laser of a multi-stripe or wide-stripe type byconverting pumped light to a fundamental wave using a solid state lasercrystal, whereby it is possible to obtain a high output harmonic wave.

[0255] Because of these factors, it is possible, for example, to obtaina total conversion efficiency of 20% by amplifying the electro-opticalconversion efficiency of the semiconductor laser of 30% with theconversion efficiency of an optical wavelength conversion element of70%. Moreover, by RF superimposing a semiconductor laser in the laserlight source of the present invention, the conversion efficiency isimproved by 5-fold, for example, as compared to the case when the RFsuperimposition is not performed.

[0256] Furthermore, with the laser projection apparatus of the presentinvention, since it is based on a semiconductor laser, it is possible toachieve considerably smaller size, lighter weight and lower cost.Moreover, it is possible to simultaneously achieve a smaller size, alighter weight and a lower cost of the apparatus by using a high outputlaser light source based on a semiconductor laser and an opticalwavelength conversion element. Furthermore, the power consumption canalso be extremely low. One of the factors therefor is that the apparatusdoes not separately has a modulator for laser light, which, instead, isintegrated with the optical wavelength conversion element. Furthermore,as compared to a conventional technique, the resolution is considerablyimproved. For example, as compared to a configuration using a gas laser,considerable improvements are achieved such as a one thousandth weight,a one-thousandth volume and a one-hundredth power consumption. The smallsize and the low power consumption of the employed laser light sourceand the integration thereof with the optical modulator greatlycontribute to these achievements. That is, this results from that theconfiguration using a semiconductor laser and an optical wavelengthconversion element can be subminiaturized while the efficiency ofconversion from an electrical power is higher than that of a gas laserby about two orders of magnitude. Particularly, it is significantlyeffective to use an element having periodic domain inverted structuresas an optical wavelength conversion element, since this makes itpossible to improve efficiency and realize integration of the opticalmodulator driven with a low voltage.

[0257] Furthermore, it is possible to generate the primary colors byallowing fluorescent substances to be irradiated with an ultravioletlaser light source, and thus to achieve an even smaller size and lowercost, thereby presenting a significant industrial advantage. Thus, it ispossible to generate the primary colors, i.e., red, green and blue, witha single laser light source. It is also favorable that the dichroicmirror for combining waves can be eliminated.

[0258] Furthermore, when scanning is terminated, the laser projectionapparatus of the present invention prevents a certain position frombeing irradiated with laser light in a concentrated manner, therebypresenting a laser light termination or cutting function. Moreover, ifthe signal from a sensor is interrupted even for a moment, the power ofthe laser light source is turned off by a control circuit. Thus, it issafe since a human, etc., never touches the short wavelength laser lighthaving a high output. The safety of this laser projection apparatus ismaintained as described above.

[0259] Furthermore, the RF superimposition is effective for a laserprojection apparatus using a laser light source based on directwavelength conversion of a semiconductor laser. This is because aspeckle noise can be prevented from being generated, whereby a clearimage can be reproduced. Moreover, a speckle noise can also be preventedin the case where red, green or blue laser light is generated directlyby semiconductor laser light.

1. A method for producing an optical element, comprising: a step offorming a proton exchange layer in an LiNb_(X)Ta_(1−X)O₃ (0≦X≦1)substrate; and an annealing step of performing a heat treatment for thesubstrate at a temperature of 120° C. or lower for 1 hour or more.
 2. Amethod for producing an optical element according to claim 1, whereinthe annealing step is performed at a temperature equal to or higher than50° C. but lower than or equal to 90° C.
 3. A method for producing anoptical element according to claim 1, wherein the annealing stepcomprises a step of gradually lowering the temperature.
 4. A method forproducing an optical element according to claim 1, wherein the step offorming the proton exchange layer comprises: a step of performing aproton exchange process for the substrate; and a step of performing aheat treatment for the substrate at a temperature of 150° C. or higher.5. A method for producing an optical element according to claim 4,wherein the annealing step is performed at a temperature equal to orhigher than 50° C. but lower than or equal to 90° C.
 6. A method forproducing an optical element according to claim 4, wherein the annealingstep comprises a step of gradually lowering the temperature.
 7. A methodfor producing an optical element according to claim 1, wherein the stepof forming the proton exchange layer comprises: a step of forming aplurality of periodically-arranged domain inverted layers in thesubstrate; and a step of forming an optical waveguide on a surface ofthe substrate.
 8. A method for producing an optical element, comprising:a step of performing a proton exchange process for an LiNb_(X)Ta_(1−X))₃(0≦X≦1) substrate; and an annealing step of performing a plurality ofheat treatments including at least first and second heat treatments forthe substrate, wherein a temperature of the second annealing is lowerthan a temperature of the first annealing by 200° C. or more.
 9. Amethod for producing an optical element according to claim 8, whereinthe second annealing is performed at a temperature equal to or higherthan 50° C. but lower than or equal to 90° C.
 10. An optical element,comprising an LiNb_(X)Ta_(1−X)O₃ (0≦X≦1) substrate and a proton exchangelayer formed in the substrate, wherein the optical element is formed ofa stable proton exchange layer such that a refractive index of theproton exchange layer does not vary with time during operation.
 11. Anoptical element according to claim 10, wherein at least a portion of theproton exchange layer forms an optical waveguide.
 12. A light sourcecomprising: a semiconductor laser; and an optical wavelength conversionelement for receiving laser light emitted from the semiconductor laserso as to convert the laser light to a harmonic wave, wherein: theoptical wavelength conversion element includes: an optical waveguide forguiding the laser light; and domain inverted structures periodicallyarranged along the optical waveguide, the optical waveguide and thedomain inverted structures being formed of a stable proton exchangelayer whose refractive index does not vary with time during operation.13. A laser light source comprising: a semiconductor laser for emittinga fundamental wave; a single mode fiber for conveying the fundamentalwave; and an optical wavelength conversion element for receiving thefundamental wave emitted from the fiber so as to generate a harmonicwave, the optical wavelength conversion element having periodic domaininverted structures.
 14. A laser light source according to claim 13,wherein the optical wavelength conversion element has a modulationfunction.
 15. A laser light source according to claim 13, wherein theoptical wavelength conversion element is formed in an LiNb_(X)Ta_(1−X)O₃(0≦X≦1) substrate.
 16. A laser light source, comprising: a semiconductorlaser for emitting a pumped light; a fiber for conveying the pumpedlight; a solid state laser crystal for receiving the pumped lightemitted from the fiber so as to generate a fundamental wave; and anoptical wavelength conversion element for receiving the fundamental waveso as to generate a harmonic wave, the optical wavelength conversionelement having periodic domain inverted structures.
 17. A laser lightsource according to claim 16, wherein the optical wavelength conversionelement has a modulation function.
 18. A laser light source according toclaim 16, wherein the optical wavelength conversion element is formed inan LiNb_(X)Ta_(1−X)O₃ (0≦X≦1) substrate.
 19. A laser light sourceaccording to claim 16, wherein the solid state laser crystal and theoptical wavelength conversion element are integrated together.
 20. Alaser light source, comprising: a semiconductor laser for emitting apumped light; a solid state laser crystal for receiving the pumped lightso as to generate a fundamental wave; a single mode fiber for conveyingthe fundamental wave; and an optical wavelength conversion element forreceiving the fundamental wave from the fiber so as to generate aharmonic wave, the optical wavelength conversion element having periodicdomain inverted structures.
 21. A laser light source according to claim20, wherein the optical wavelength conversion element has a modulationfunction.
 22. A laser light source, comprising: a distributed feedbacktype semiconductor laser for emitting laser light; a semiconductor laseramplifier for amplifying the laser light; and an optical wavelengthconversion element for receiving the amplified laser light so as togenerate a harmonic wave, the optical wavelength conversion elementhaving periodic domain inverted structures.
 23. A laser light sourceaccording to claim 22, wherein the optical wavelength conversion elementhas a modulation function.
 24. A laser light source according to claim22, wherein the optical wavelength conversion element is formed in anLiNb_(X)Ta_(1−X)O₃ (0≦X≦1) substrate.
 25. A laser light source accordingto claim 22, wherein the semiconductor laser is wavelength-locked.
 26. Alaser light source, comprising: a semiconductor laser for emitting laserlight; and an optical wavelength conversion element in which periodicdomain inverted structures and an optical waveguide are formed, whereina width and a thickness of the optical waveguide are each 40 μm orgreater.
 27. A laser light source according to claim 26, wherein theoptical wavelength conversion element has a modulation function.
 28. Alaser light source according to claim 26, wherein the optical wavelengthconversion element is formed in an LiNb_(X)Ta_(1−X)O₃ (0≦X≦1) substrate.29. A laser light source according to claim 26, wherein the opticalwaveguide is of a graded type.
 30. A laser device, comprising: a laserlight source having a semiconductor laser for radiating laser light andan optical wavelength conversion element for generating a harmonic wavebased on the laser light; a modulator for modulating an output intensityof the harmonic wave; and a deflector for changing a direction of theharmonic wave emitted from the laser light source, wherein periodicdomain inverted structures are formed in the optical wavelengthconversion element.
 31. A laser device according to claim 30, whereinthe laser light source comprises: a single mode fiber for conveyinglaser light from the semiconductor laser to the optical wavelengthconversion element.
 32. A laser light source according to claim 30,wherein the laser light source comprises: a fiber for conveying laserlight from the semiconductor laser; and a solid state laser crystal forreceiving laser light emitted from the fiber so as to generate afundamental wave.
 33. A laser light source according to claim 30,wherein: the semiconductor laser device is a distributed feedback typesemiconductor laser; and the laser light source further comprises asemiconductor laser amplifier for amplifying the laser light from adistributed feedback type semiconductor laser.
 34. A laser light sourceaccording to claim 30, wherein: an optical waveguide is formed in theoptical wavelength conversion element; and a width and a thickness ofthe optical waveguide are each 40 μm or greater.
 35. A laser device,comprising: a laser light source for radiating modulated ultravioletlaser light; and a deflector for changing a direction of the ultravioletlaser light, wherein: the deflector irradiates a screen with theultraviolet laser light so as to generate red, green or blue light froma fluorescent substance being applied on the screen.
 36. A laser deviceaccording to claim 35, wherein the laser light source comprises: asemiconductor laser; an optical wavelength conversion element forgenerating a harmonic wave; and a single mode fiber for conveying laserlight from the semiconductor laser to the optical wavelength conversionelement.
 37. A laser light source according to claim 35, wherein thelaser light source comprises: a semiconductor laser; a fiber forconveying laser light from the semiconductor laser; a solid state lasercrystal for receiving laser light emitted from the fiber so as togenerate a fundamental wave; and an optical wavelength conversionelement for generating a harmonic wave from the fundamental wave.
 38. Alaser light source according to claim 35, wherein the laser light sourcefurther comprises: a semiconductor laser; and a semiconductor laseramplifier for amplifying laser light from a distributed feedback typesemiconductor laser.
 39. A laser light source according to claim 35,wherein the laser light source comprises: a semiconductor laser foremitting laser light; and an optical wavelength conversion element inwhich an optical waveguide for guiding the laser light and periodicdomain inverted structures are formed, wherein a width and a thicknessof the optical waveguide are each 40 μm or greater.
 40. A laser device,comprising: three laser light sources respectively for generating red,green and blue laser light beams; a modulator for changing an intensityof each of the laser light beams; and a deflector for changing adirection of each of the laser light beams, wherein the laser lightsource is formed of a semiconductor laser.
 41. A laser device accordingto claim 40, wherein the laser light source comprises: a semiconductorlaser; an optical wavelength conversion element for generating aharmonic wave; and a single mode fiber for conveying laser light fromthe semiconductor laser to the optical wavelength conversion element.42. A laser light source according to claim 40, wherein the laser lightsource comprises: a semiconductor laser; a fiber for conveying laserlight from the semiconductor laser; a solid state laser crystal forreceiving laser light emitted from the fiber so as to generate afundamental wave; and an optical wavelength conversion element forgenerating a harmonic wave from the fundamental wave.
 43. A laser lightsource according to claim 40, wherein the laser light source furthercomprises: a semiconductor laser; and a semiconductor laser amplifierfor amplifying laser light from a distributed feedback typesemiconductor laser.
 44. A laser light source according to claim 40,wherein the laser light source comprises: a semiconductor laser foremitting laser light; and an optical wavelength conversion element inwhich an optical waveguide for guiding the laser light and periodicdomain inverted structures are formed, wherein a width and a thicknessof the optical waveguide are each 40 μm or greater.
 45. A laser device,comprising: at least one laser light source including a semiconductorlaser; a sub-semiconductor laser; a modulator for changing an intensityof light from the laser light source; a screen; and a deflector forchanging a direction of light from the laser light source so as to scanthe screen with the light, wherein: light emitted from thesub-semiconductor laser scans a peripheral portion of the screen; andradiation of laser light from the laser light source is terminated whenan optical path of the light emitted from the sub-semiconductor laser isblocked.
 46. A laser device according to claim 45, wherein the laserlight source comprises: an optical wavelength conversion element forgenerating a harmonic wave; and a single mode fiber for conveying laserlight from the semiconductor laser to the optical wavelength conversionelement.
 47. A laser light source according to claim 45, wherein thelaser light source comprises: the semiconductor laser; a fiber forconveying laser light from the semiconductor laser; a solid state lasercrystal for receiving laser light emitted from the fiber so as togenerate a fundamental wave; and an optical wavelength conversionelement for generating a harmonic wave from the fundamental wave.
 48. Alaser light source according to claim 45, wherein: the semiconductorlaser is a distributed feedback type semiconductor laser; and the laserlight source further comprises a semiconductor laser amplifier foramplifying laser light from the distributed feedback type semiconductorlaser.
 49. A laser light source according to claim 45, wherein the laserlight source comprises: an optical wavelength conversion element inwhich an optical waveguide for guiding laser light from thesemiconductor laser and periodic domain inverted structures are formed,wherein a width and a thickness of the optical waveguide are each 40 μmor greater.
 50. A laser device, comprising: at least one laser lightsource including a semiconductor laser; a deflector for changing adirection of laser light radiated from the laser light source so as toscan the screen with the laser light, wherein: the device furthercomprises two or more detectors for generating a signal when receiving aportion of the laser; and generation of laser light from the laser lightsource is terminated when the detector does not generate a signal for acertain period of time while the deflector scans the screen with thelaser light.
 51. A laser device according to claim 50, wherein the laserlight source comprises: an optical wavelength conversion element forgenerating a harmonic wave; and a single mode fiber for conveying laserlight from the semiconductor laser to the optical wavelength conversionelement.
 52. A laser light source according to claim 50, wherein thelaser light source comprises: the semiconductor laser; a fiber forconveying laser light from the semiconductor laser; a solid state lasercrystal for receiving laser light emitted from the fiber so as togenerate a fundamental wave; and an optical wavelength conversionelement for generating a harmonic wave from the fundamental wave.
 53. Alaser light source according to claim 50, wherein: the semiconductorlaser is a distributed feedback type semiconductor laser; and the laserlight source further comprises a semiconductor laser amplifier foramplifying laser light from the distributed feedback type semiconductorlaser.
 54. A laser light source according to claim 50, wherein the laserlight source comprises: an optical wavelength conversion element inwhich an optical waveguide for guiding laser light from thesemiconductor laser and periodic domain inverted structures are formed,wherein a width and a thickness of the optical waveguide are each 40 μmor greater.
 55. A laser device, comprising: at least one laser lightsource including a semiconductor laser; a modulator for changing anintensity of each laser light; and a deflector for changing a directionof each laser light, wherein laser light emitted from the laser lightsource is split into two or more optical paths so as to irradiate ascreen from two directions.
 56. A laser device according to claim 55,wherein the laser light source comprises: an optical wavelengthconversion element for generating a harmonic wave; and a single modefiber for conveying laser light from the semiconductor laser to theoptical wavelength conversion element.
 57. A laser light sourceaccording to claim 55, wherein the laser light source comprises: thesemiconductor laser; a fiber for conveying laser light from thesemiconductor laser; a solid state laser crystal for receiving laserlight emitted from the fiber so as to generate a fundamental wave; andan optical wavelength conversion element for generating a harmonic wavefrom the fundamental wave.
 58. A laser light source according to claim55, wherein: the semiconductor laser is a distributed feedback typesemiconductor laser; and the laser light source further comprises asemiconductor laser amplifier for amplifying laser light from thedistributed feedback type semiconductor laser.
 59. A laser light sourceaccording to claim 55, wherein the laser light source comprises: anoptical wavelength conversion element in which an optical waveguide forguiding laser light from the semiconductor laser and periodic domaininverted structures are formed, wherein a width and a thickness of theoptical waveguide are each 40 μm or greater.
 60. A laser deviceaccording to claim 55, wherein: two optical paths are formed by twolaser light sources; and the laser light sources respectively experiencedifferent modulations.
 61. A laser device according to claim 55, whereinthe two optical paths are switched with each other based on time.
 62. Alaser device, comprising: at least one laser light source including asemiconductor laser; a first optical system for setting laser lightemitted from the laser light source into a parallel beam; a liquidcrystal cell for spatially modulating the parallel beam; and a secondoptical system for irradiating a screen with light emitted from theliquid crystal cell.
 63. A laser device according to claim 62, whereinthe laser light source comprises: an optical wavelength conversionelement for generating a harmonic wave; and a single mode fiber forconveying laser light from the semiconductor laser to the opticalwavelength conversion element.
 64. A laser light source according toclaim 62, wherein the laser light source comprises: the semiconductorlaser; a fiber for conveying laser light from the semiconductor laser; asolid state laser crystal for receiving laser light emitted from thefiber so as to generate a fundamental wave; and an optical wavelengthconversion element for generating a harmonic wave from the fundamentalwave.
 65. A laser light source according to claim 62, wherein: thesemiconductor laser is a distributed feedback type semiconductor laser;and the laser light source further comprises a semiconductor laseramplifier for amplifying laser light from the distributed feedback typesemiconductor laser.
 66. A laser light source according to claim 62,wherein the laser light source comprises: an optical wavelengthconversion element in which an optical waveguide for guiding laser lightfrom the semiconductor laser and periodic domain inverted structures areformed, wherein a width and a thickness of the optical waveguide areeach 40 μm or greater.
 67. A laser device according to claim 45, whereinthe sub-semiconductor laser is an infrared laser.
 68. A laser deviceaccording to claim 45, wherein laser light radiation is terminated byshifting a phase-matched wavelength of the optical wavelength conversionelement.
 69. An optical disk apparatus, comprising: a laser light sourcefor generating laser light; an optical wavelength conversion element forconverting a fundamental wave to a harmonic wave; an optical pickupincorporating therein the optical wavelength conversion element; and anactuator for moving the optical pickup, wherein the laser light radiatedfrom the laser light source is incident upon the optical pickup via anoptical fiber.
 70. An optical disk apparatus according to claim 69,wherein the laser light source includes a semiconductor laser disposedoutside the optical pickup.
 71. An optical disk apparatus according toclaim 70, wherein the laser light source further comprises a solid statelaser crystal for generating a fundamental wave using laser lightemitted from the semiconductor laser as pumped light.
 72. An opticaldisk apparatus according to claim 71, wherein: the solid state lasercrystal is disposed outside the optical pickup; and the fundamental wavegenerated by the solid state laser medium is incident upon the opticalwavelength conversion element via the optical fiber.
 73. An optical diskapparatus according to claim 71, wherein: the solid state laser crystalis disposed inside the optical pickup; and the laser light emitted fromthe semiconductor laser is incident upon the solid state laser via theoptical fiber.
 74. A laser light source according to claim 30, wherein aharmonic wave is superimposed over the semiconductor laser duringoperation.
 75. A laser light source according to claim 40, wherein aharmonic wave is superimposed over the semiconductor laser duringoperation.